Lithium Parallel In Harmony With Lead Acid

[BatteryMegaUK]

Hi, can you tell us how you tested this? for instance how many charge discharge cycles over what period of time and the condition of each battery at the end of the test. I think people investing in expensive lithium batteries would want to know they are not shortening the life of the battery by using an incorrect charging regime.

Hi there

Thanks for your question!

We completed 16 cycles in total with the batteries wired correctly in parallel (not daisy chained, but cross wired which is crucial for lead or lithium). 8 cycles were recharged on a Victron charger “lithium setting” and 8 cycles were recharged on the “lead acid settings”? The purpose for this was to check lithium received a full charge and that the lead acid was not over charged. Both were as we'd expected and we shared our results with TN who confirmed and said actually at a lower charge voltage the lithium will actually last longer than spec.

The discharge was on our Astratec discharge tester which applies 20amp load continuously until the 190ah (rating for combined ah) was reach. Each test passed, which is great as Astratec finds any faults, they simply can’t hide from it.

You may all like to know we have a lot of TN power on test in the commercial market and they have all passed with flying colours, we have also submitted it for testing with the NHS. The range is expanding, it cost around $10k to UN38.3 each part number which is why we didn’t launch the whole range at once, but we will soon have 12ah,24ah,33ah, 54ah, 84ah,100ah, 110ah

 

[eddie]

I can think of a number of issues with this. But the one that would concern me the most is...
As a Pb battery discharges it's voltage falls. Whereas a Li battery will maintain an almost constant voltage across the bulk of it's discharge range.
As the Pb battery voltage lowers the Li battery will then start charging the Pb battery. This is wasteful as it is not efficient to charge Pb battery at all.
The other possibility is that as the Li battery has a higher voltage it will provide more power and go through it's full discharge cycle long before the Pb battery reaches 60%.

I am never happy mixing manufacturers or age, never mind chemistry.

Yes it might work, but in my opinion it is far far from advisable...

I (as normal) 100% agree with Gromett.

Also with the greatest respect, charging a couple of batteries in parallel, on a bench for a few days playing with a multi meter cannot seriously be taken as a "test"

I have mixed all battery types in the past (except Lithium) just to get capacity on my own motorhomes with no real ill effect, but! I have the advantage of understanding what I am doing and have some expensive test equipment so would regularly test my batteries too ensure that if one was failing or playing up I could deal with it whilst my van was still in the workshop and not fail causing me major grief whilst on Corsica! There is no way that I would allow any of our staff to mix battery types on any of our installations for a customer, it is asking for trouble, trouble that may on materialise some time down the road.

Batteries in parallel, that have significant charge and discharge characteristics must by nature play havoc with the ancillary equipment. Take an inverter for example, installed correctly it will be connected to the positive one end of the bank and the negative the other end of the bank. Draw 100 amps and the Lithium will deliver much more than the conventional battery, and equally when the bank in recharged the Lithium will accept a much higher charge much quicker than the conventional battery, and once charged will potentially turn off the charger before the conventional battery reaches maximum charge. Being in Parallel, the voltage will eventually equalise, by a sacrificial discharge from the Lithium leaving neither 100% charged. I can foresee lots of other potential issues in the real world.

I started my working life working for the Longlife Tyre & Battery Company and as the junior it was my job to make whatever battery was ordered in the shop that day, starting with soldering the lead plates, sealing the cases with bitchumen and filling with Sulfuric Acid delivered to us in glass carboys, so I've built a few. I have even ended up in the eye hospital in Plymouth when one blew up in my face when testing (and yes I was wearing goggles)

 

[Minxy]

If you are worried about someone making a mistake then use the full technical name if you wish. But I'll just refer to them as lithium

... but you know what you are talking about ... well most of the time I think!

 

[Wildbill]

Hi there

Thanks for your question!

We completed 16 cycles in total with the batteries wired correctly in parallel (not daisy chained, but cross wired which is crucial for lead or lithium). 8 cycles were recharged on a Victron charger “lithium setting” and 8 cycles were recharged on the “lead acid settings”? The purpose for this was to check lithium received a full charge and that the lead acid was not over charged. Both were as we'd expected and we shared our results with TN who confirmed and said actually at a lower charge voltage the lithium will actually last longer than spec.

The discharge was on our Astratec discharge tester which applies 20amp load continuously until the 190ah (rating for combined ah) was reach. Each test passed, which is great as Astratec finds any faults, they simply can’t hide from it.

You may all like to know we have a lot of TN power on test in the commercial market and they have all passed with flying colours, we have also submitted it for testing with the NHS. The range is expanding, it cost around $10k to UN38.3 each part number which is why we didn’t launch the whole range at once, but we will soon have 12ah,24ah,33ah, 54ah, 84ah,100ah, 110ah

When you have done 10.000,000 cycles and proven every thing works and worn you shelf out i am sure that someone will come along to shoot you down in flames.
even if you are a expert in something theirs always someone on a forum who know's better
some even know more than the manufacturers them shelf
good luck with your research
You will find that battery snobbery is a big thing on forums me i just go to the scrap yard
bill

 

[BatteryMegaUK]

Clear something up please. In the average (older) Motorhome setup, it is only the charging phase that has all the batteries connected (by whatever means)?. Therefore under load conditions (discharging) the Chassis Battery should be unaffected? Otherwise, one could be in a situation where the vehicle will not have sufficient capacity to start?. Any true BtoB charge system the flow would be determined by the monitoring "software" with the intention of compensating for "Ghost" drains, E.g. Clocks and other background drains.

Hi there,

Depending on your set up, your start battery is likely to be eventually connected to the house battery when the start battery is being charged. The delay will depend on the equipment you are using (for example a Voltage Sensitive Relay may have a time delay to avoid relay chatter). Likewise, when discharging your house battery, the start battery may be slightly discharged before the VSR (voltage sensitive relay) opens to ensure enough charge is in the start battery to be able to start the vehicle. Some vehicles use split charge or battery to battery chargers that are linked to the ignition so that the house battery only connects to the start battery under charge only conditions. However, as you can see, both banks are connected for short periods in both charge and discharge cycles in a majority of cases where split charge relays are being used.

Battery Megastore.

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[BatteryMegaUK]

Or better still.... What guarantee will you give to your research and advise.
If someone destroys their lithium battery or Flooded battery after taking your advise will you replace it even if you didn't supply it?

We can’t give guarantees on system we have never seen, have no idea of the quality of the instillation or even if the lead acid battery is even already faulty, it would be commercially a crazy thing to do especially when we have already dramatically reduce the price to members (which won’t last forever I am afraid )

However we are willing to share our test information as some may find it helpful. We can also perform most test if anyone wants to know anything in connection to lithium.

 

[eddie]

VSR's (Voltage Sensing Relays) used for what we all euphemistically call "split charge" are only used by people that don't truly understand what they are doing or are lazy.

The reason that I say this is that on paper a VSR makes for a quicker easier installation, however, if you are a motorhome specialist or use a motorhome yourself (me being both) I know that I will want to charge my engine batteries, dual solar charging for example, and on a nice sunny day, the threshold voltage of the VSR is reached and as the VSR "thinks" that the engine is running it tries to charge the leisure battery and all sorts of weird things happen.

AutoSleepers had an issue a couple of years ago, where they for some reason had used a VSR and on a sunny day, the the solar regulator would attempt to charge the engine battery, the VSR as the threshold voltage was reached, thought that the engine was running, and the Sargent unit turned off all of the habitation electrics, as if the motorhome was being driven! It did take us some working out what was going wrong, but we got there in the end.

This is a typical VSR (I've been walking around taking pictures of random stuff and everyone thinks I've gone mad)

There are different makes and different voltage ranges, but it is much better to make a physical connection, so it only works when it is "meant" to work

A relay connected to D+ output on the alternator will only close (make work) when the engine is running and the alternator is charging. This way if the leisure battery is flat, the relay will remain open (not working) until the engine is running.

What this means in real terms is that you turn on the ignition, nothing happens, you start the engine, still nothing happens, and once the alternator is working, the relay starts to do its job and your leisure battery starts to charge.

Sometimes we will see a system where the relay has been connected, just to an ignition switch controlled supply (the wire goes "live" as soon as the ignition is on but the engine isn't started), The trouble with this way is that when you turn on the ignition the leisure battery immediately tries to charge from the engine battery, and then when you crank the starter motor will try to pull power from the engine and leisure batteries, potentially blowing fuses and causing all sorts of problems (just think about the thickness of the wire from the engine battery to the starter motor, then think about the thickness of the wire on the leisure battery!)

So if you have a relay controlled split charge, connected to the D+ your engine and leisure batteries are in parallel (connected together) when the engine is running and the they will both charge, but there will be a voltage difference due to distance and wire gauge.

This is an example of a "good" relay that could be used on the left and the picture on the right show

common or garden relays that are "normally

used.

Often big shiny boxes with loads of wires in and out will only have a couple of common relays internally and people assume that they have a sophisticated charging system when sadly they don't







This is the "guts" of a "all in one "system used in lots of motorhomes, you can see the two black relays. One is the split charge relay and one is the fridge relay (we assume) you can also see the "built in" solar regulator and "heavy duty" wiring

Better is a dedicated Battery to Battery device which will, on start, check the state of the engine battery, and once satisfied all is OK will then direct the charge towards the leisure battery(s)

Or, the American way is to re-jig it all completely and connect the output of the alternator to a special diode pack and then connect the engine and the auxiliary batteries (what the Yanks call leisure batteries) and then the diode pack sorts it all out

 

[BatteryMegaUK]

VSR's (Voltage Sensing Relays) used for what we all euphemistically call "split charge" are only used by people that don't truly understand what they are doing or are lazy.

The reason that I say this is that on paper a VSR makes for a quicker easier installation, however, if you are a motorhome specialist or use a motorhome yourself (me being both) I know that I will want to charge my engine batteries, dual solar charging for example, and on a nice sunny day, the threshold voltage of the VSR is reached and as the VSR "thinks" that the engine is running it tries to charge the leisure battery and all sorts of weird things happen.

AutoSleepers had an issue a couple of years ago, where they for some reason had used a VSR and on a sunny day, the the solar regulator would attempt to charge the engine battery, the VSR as the threshold voltage was reached, thought that the engine was running, and the Sargent unit turned off all of the habitation electrics, as if the motorhome was being driven! It did take us some working out what was going wrong, but we got there in the end.

This is a typical VSR (I've been walking around taking pictures of random stuff and everyone thinks I've gone mad)
View attachment 327734

There are different makes and different voltage ranges, but it is much better to make a physical connection, so it only works when it is "meant" to work

A relay connected to D+ output on the alternator will only close (make work) when the engine is running and the alternator is charging. This way if the leisure battery is flat, the relay will remain open (not working) until the engine is running.

What this means in real terms is that you turn on the ignition, nothing happens, you start the engine, still nothing happens, and once the alternator is working, the relay starts to do its job and your leisure battery starts to charge.

Sometimes we will see a system where the relay has been connected, just to an ignition switch controlled supply (the wire goes "live" as soon as the ignition is on but the engine isn't started), The trouble with this way is that when you turn on the ignition the leisure battery immediately tries to charge from the engine battery, and then when you crank the starter motor will try to pull power from the engine and leisure batteries, potentially blowing fuses and causing all sorts of problems (just think about the thickness of the wire from the engine battery to the starter motor, then think about the thickness of the wire on the leisure battery!)

So if you have a relay controlled split charge, connected to the D+ your engine and leisure batteries are in parallel (connected together) when the engine is running and the they will both charge, but there will be a voltage difference due to distance and wire gauge.

This is an example of a "good" relay that could be used on the left and the picture on the right showView attachment 327735 common or garden relays that are "normallyView attachment 327742
used.

Often big shiny boxes with loads of wires in and out will only have a couple of common relays internally and people assume that they have a sophisticated charging system when sadly they don't







This is the "guts" of a "all in one "system used in lots of motorhomes, you can see the two black relays. One is the split charge relay and one is the fridge relay (we assume) you can also see the "built in" solar regulator and "heavy duty" wiring

View attachment 327744


Better is a dedicated Battery to Battery device which will, on start, check the state of the engine battery, and once satisfied all is OK will then direct the charge towards the leisure battery(s)

View attachment 327745


Or, the American way is to re-jig it all completely and connect the output of the alternator to a special diode pack and then connect the engine and the auxiliary batteries (what the Yanks call leisure batteries) and then the diode pack sorts it all out

View attachment 327746

The VSR has it's drawbacks however is cheap and cheerful for those that prefer more control we offer Sterling or Victron battery to battery chargers for great prices.

 

[PeteH]

One special issue with R-V`s, They are more often setup in my experience, to use wet (Auto) batteries in both the chassis and house situations. The Yanks often do not fit "Deep Cycle" house batteries instead using standard "auto" batteries in both so the charging regime is not so critical. Whereas my current Rapido came with 2 Gel house batteries. But the Chassis Battery is not. It may be AGM, but unless or until I remove half the floor I won`t actually know!. The charging / management unit is SCHEIBER 30.69200.12. BTW. There being no information with the coach.

 

[Vic. Parsons.]

Just a quick point for Battery megastore.

Having used LiPo batteries in the past with RC helicopters, I came to understand that cycle life can be adversely affected by always charging to 100% or around 4.2v per cell. Since the chargers I used had balance leads, I could see the charge of individual cells to watch for cells that were underperforming and also set the charge cut-off voltage.
Similarly, with LiFe which would have a voltage of around 4.2 at 100% charge, if the battery is always fully charged to this level, the cycle life will be reduced quite considerably.
If the same battery were only ever charged to around 3.92v per cell instead of 4.2v, the cycle life would be greatly extended, by as much as 5 times. Also, the difference in battery capacity between 3.92v and 4.2v is pretty negligible when weighed against the longevity of the battery.
So, I'm just curious to know, do the chargers being used for your tests charge to 4.2v per cell for 100% capacity or is it managed to charge for extended battery life by charging as full being 3.92v per cell?

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[BatteryMegaUK]

Just a quick point for Battery megastore.

Having used LiPo batteries in the past with RC helicopters, I came to understand that cycle life can be adversely affected by always charging to 100% or around 4.2v per cell. Since the chargers I used had balance leads, I could see the charge of individual cells to watch for cells that were underperforming and also set the charge cut-off voltage.
Similarly, with LiFe which would have a voltage of around 4.2 at 100% charge, if the battery is always fully charged to this level, the cycle life will be reduced quite considerably.
If the same battery were only ever charged to around 3.92v per cell instead of 4.2v, the cycle life would be greatly extended, by as much as 5 times. Also, the difference in battery capacity between 3.92v and 4.2v is pretty negligible when weighed against the longevity of the battery.
So, I'm just curious to know, do the chargers being used for your tests charge to 4.2v per cell for 100% capacity or is it managed to charge for extended battery life by charging as full being 3.92v per cell?

The chargers we used are Victron energy chargers - these were charged on both lead acid and lithium settings and via the Victron app, you can keep an eye on the voltages.

You will see in both settings the charger goes through a whole range of different voltages so its not as simple as saying they charge at a specific voltage for the entire charge.

You are correct that if you reduce the charge voltage they will last longer but remember even at 14.6 (+-0.2) they will do over 5000 cycles. TN Power have to set their specification, this was at 14.6v but you can deviate from this.

It’s important to remember that with lithium not all BMS are the same and this depends on the quality of the BMS - this will ultimately dictate the cycle life of the batteries and the discharge level.

 

[SomeoneElse]

No mention of the temperature that these tests were conducted.
The big difference between decent chargers is the LA ones would ramp up the voltage as the temperature drops and can reach 15V at zero degrees, whereas a lithium one would reduce the charging rate as the temperature approaches zero. You may get away with mixing technologies at room temperature but "extreme" temperatures one of the batteries is likely to be a very unhappy bunny.

 

[BatteryMegaUK]

No mention of the temperature that these tests were conducted.
The big difference between decent chargers is the LA ones would ramp up the voltage as the temperature drops and can reach 15V at zero degrees, whereas a lithium one would reduce the charging rate as the temperature approaches zero. You may get away with mixing technologies at room temperature but "extreme" temperatures one of the batteries is likely to be a very unhappy bunny.

All the tests were performed at room temperature, Victron is regarded as the leading DC power electronics manufacture & the maximum output from their chargers is 14.7 which both the lead acid & the lithium could deal with. It is a good point that lithium should not really be recharged unless over zero degrees. You should find a lot of chargers with temperature sensors will not charge below zero degrees in lithium mode.

 

[pappajohn]

We can’t give guarantees on system we have never seen, have no idea of the quality of the instillation or even if the lead acid battery is even already faulty, it would be commercially a crazy thing to do especially when we have already dramatically reduce the price to members (which won’t last forever I am afraid )

However we are willing to share our test information as some may find it helpful. We can also perform most test if anyone wants to know anything in connection to lithium.

So what you're saying is.... Its OK for us to do it as we have the equipment and facilities to monitor these tests but if you mix batteries the results could be very different and you may destroy a very expensive battery but that's not our fault.
You're claiming its safe to mix lead and lithium..... But only in 'laboratory' conditions.

 

[BatteryMegaUK]

So what you're saying is.... Its OK for us to do it as we have the equipment and facilities to monitor these tests but if you mix batteries the results could be very different and you may destroy a very expensive battery but that's not our fault.
You're claiming its safe to mix lead and lithium..... But only in 'laboratory' conditions.

No, we are saying if you want to mix lead acid and lithium you can (should you want to, we are not saying you should, every system and requirements are different) but only if you meet the following criteria

1. The wring must be correct (not daisy chained)
2. Correct charging equipment set at acceptable voltages
3. You must stay within the designed limits of both batteries including how often batteries are recharged

Please note lead acid should only be discharged to 50% DOD, and lithium is 90% DOD,once they have been joined you are restricted to 50% DOD, any more and damage will occur to the lead acid. Remember Lithium can cope with PSOC but lead acid is does not have true PSOC capabilities (partial state of charge)

As we can’t be responsible for elements we have no control over.

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[SomeoneElse]

All the tests were performed at room temperature, Victron is regarded as the leading DC power electronics manufacture & the maximum output from their chargers is 14.7 which both the lead acid & the lithium could deal with. It is a good point that lithium should not really be recharged unless over zero degrees. You should find a lot of chargers with temperature sensors will not charge below zero degrees in lithium mode.

Interesting you mention a Victron charger as my Votronic charger has as one of its four Lithium settings especially for "Victron LFP-BMS 12,8" batteries and that has a maximum voltage of 14.2V. Is this ability to mix LeadAcid and Lithium batteries limited to specific types and makes of batteries and specific settings for specific chargers.

 

[weejocky]

Please note lead acid should only be discharged to 50% DOD, and lithium is 90% DOD,once they have been joined you are restricted to 50% DOD, any more and damage will occur to the lead acid. Remember Lithium can cope with PSOC but lead acid is does not have true PSOC capabilities (partial state of charge)

So what is the point of this thread

 

[pappajohn]

Please note lead acid should only be discharged to 50% DOD, and lithium is 90% DOD,once they have been joined you are restricted to 50% DOD, any more and damage will occur to the lead acid

So what you're saying is joining a lead and a lithium restricts you to 50% DOD overall.
May as well use a pair of lead acid batteries then and save a few hundred quid or spend it on even more FLA batteries for an even bigger Bank.

 

[funflair]

No, we are saying if you want to mix lead acid and lithium you can (should you want to, we are not saying you should, every system and requirements are different) but only if you meet the following criteria

1. The wring must be correct (not daisy chained)
2. Correct charging equipment set at acceptable voltages
3. You must stay within the designed limits of both batteries including how often batteries are recharged

Please note lead acid should only be discharged to 50% DOD, and lithium is 90% DOD,once they have been joined you are restricted to 50% DOD, any more and damage will occur to the lead acid. Remember Lithium can cope with PSOC but lead acid is does not have true PSOC capabilities (partial state of charge)

As we can’t be responsible for elements we have no control over.

I thought that lithium held its voltage as it discharged so would the lead acid not stay charged well above 50% to the end of the lithiums natural cycle,

Martin

 

[Pausim]

I thought that lithium held its voltage as it discharged so would the lead acid not stay charged well above 50% to the end of the lithiums natural cycle,

Martin

Yes. If the discharge curve for my Relion LiFePO4 is correct then at a 20A rate of discharge it would still be showing 12.5V when 90% discharged. By the time the lead acid reaches 50% discharged at 12.2V the lithium will be into the damage zone, so basically the lithium will have to do all the work and be damaged if you use anything much from the lead one. I most certainly will not be risking my lithium battery for a very questionable additional contribution from a lead one. Also the built in battery management system of the lithium battery could be confused by the voltage from the lead one and fail to protect it and as for cell balancing ????

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[thebriars]

All rather academic given the ongoing research into improved lithium batteries that will replace all the current lithium technologies. I'll stick with my lead acid until these arrive which they surely will within a few years.

 

[thebriars]

Please note lead acid should only be discharged to 50% DOD, and lithium is 90% DOD,once they have been joined you are restricted to 50% DOD, any more and damage will occur to the lead acid.

This old chestnut again. Damage occurs to every rechargeable battery no matter what the chemistry every time it is charged and discharged. Please, BMUK if you are seeking to be credible, stick to scientific facts not glib crude statements than need numerous qualifiers to become anything like accurate.

 

[HandyAndy]

I thought that lithium held its voltage as it discharged so would the lead acid not stay charged well above 50% to the end of the lithiums natural cycle,

Martin

voltage is voltage. If the lithium is "used" down to 12.5v then so will the lead acid.
Now while the work of the CURRENT draw will come from the lithium, the over all voltage will stay the same or similar. if one were to drift off from the other the lower voltage one would be topped up by the higher voltage one til they balanced themselves back out.

The easiest way of thinking about the way batteries work is to think of the energy as water and the cables as pipes.
A lead acid has a small tank and a small pipe
A lithium has a big tank and a big pipe.
While the water may pour quicker from the lithium, the level between the two will remain constant as they are joined

 

[Pausim]

While the water may pour quicker from the lithium, the level between the two will remain constant as they are joined

Yes the voltage will balance but because the Li operates at a higher voltage, which equates to higher pressure in your water analogy, it will empty itself into the Pb one. You then can’t draw on the power saved into the Pb one without damaging the Li one by reducing it’s voltage below the safe level.

If you want to use a water analogy you need to think of the 2 tanks being mounted at different levels in a sealed system. The higher tank empties into the lower one but when you start to use the water from the lower tank the negative pressure collapses the higher tank.

 

[BatteryMegaUK]

So what is the point of this thread

In previous posts funsters were worried if they added a lithium to a vehicle that had a relay that the lithium would damage the lead acid starter battery. This test shows it wont.

Although there is little again in Ah you would still gain the cycles from the Lead acid battery, so if you want lithium now and have a healthy lead acid battery you can link, use and benefit from this until the lead acid comes to the end of its life and go 100% lithium.

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[BatteryMegaUK]

This old chestnut again. Damage occurs to every rechargeable battery no matter what the chemistry every time it is charged and discharged. Please, BMUK if you are seeking to be credible, stick to scientific facts not glib crude statements than need numerous qualifiers to become anything like accurate.

Damage does not occur every time a battery is discharged, active material is used on every cycle - there is a massive difference. Damage is different; you don’t need to worry if we are credible the facts are from the manufactures and the information is already published by them.

 

[weejocky]

Although there is little again in Ah you would still gain the cycles from the Lead acid battery, so if you want lithium now and have a healthy lead acid battery you can link, use and benefit from this until the lead acid comes to the end of its life and go 100% lithium.

So I have my healthy lead acid already I can just add the lithium to it and all will be well, but I won't get the benefits of lithium until my lead acid dies. Sorry mate the only person to benefit here is the bloke selling the batteries.

 

[BatteryMegaUK]

So I have my healthy lead acid already I can just add the lithium to it and all will be well, but I won't get the benefits of lithium until my lead acid dies. Sorry mate the only person to benefit here is the bloke selling the batteries.

Hi,

In a bank you will have 10% more capacity and all the additional life cycles from the lead acid. You will be able to draw the power faster, but you are limited to 50% DOD and the batteries will work far better in PSOC (Partial State Of Charge) than the lead acid ever could on its own.

However this was not the point, there was concern from people on the forum saying that you can’t put lead acid and lithium together and all motorhomes have a lead acid starter so it is important for us to show that this is actually incorrect - so we ran the test and shared the information.

If you want to stick to lead acid you can and if you want lithium you can - we cater for both.

 

[Richard n Ann]

Glad I bought gel ??

 

[Pausim]

I have just taken delivery of a new motorhome and at present I have my LIFePO4 sitting next to the original Gel one which is currently doing all the work. When I have resolved some issues between my B2B and the operation of the parallel relay I will transfer over to the Li and remove the Gel, saving 28KG of weight. At no point do I intend to run the two in parallel. However, this topic interests me so I have contacted Relion to get their opinion.

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