Keeping LiFePo4 Lithium at 100%

[Mike001]

So, as the title says...

I ask this as our Motorhome is our "grab bag" in case of emergency so is always kept at over 95% charge.

How much does it actually decrease the life of the lithium battery?
Would it half the life, 10% less, 20% ? Or is it more like, how long is a piece of string.
Have there been any actual tests done? I assume there have been but its hard to find any information of actual "battery life that is lost"

I have a 400ah lithium. After, say, 3 years what would it be at then? I guess I need to do capacity tests yearly or something.
One of lifes mysteries I guess

 

[Jimbohorlicks]

So when you jump into your van and its " only" at 90% do you say to yourself. I wont bother going out in the van because I' ve only got 360 ah of useable charge left?
What does it really matter. There's enough in the batteries to get you to where you want to go and more.
If your concerned that 100% charge may damage them. Drop them to 90% it won't affect your lifestyle.
They soon charge back up again.

 

[Mike001]

Its really more of a question as to how much in real life it actually reduces capacity by.
Would never stop me from going out.
Is one of those "does it really matter that much?" type of question. Curiosity is all.

 

[Abacist]

Surely your B2B will top them up en route? If you have no B2B then that’s the answer!

 

[fat haggis]

I just leave them to do what they do. Same as Jim. I to have 400ah lifepo4.

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[Mike001]

Yep, I understand what you all are saying, and that is what I do.
B2B charges up when moving, also have an onboard 1200 watt genny to power a 50amp Lithium battery charger if required.
I was really more wondering what life reduction keeping the battery at close to 100% would actually do.
All purely as I have never seen any documentation or info on damage (if any) that is done.
As I said. It is only out of curiosity.

 

[Guigsy]

There's not a lot of data because the effect isn't that great. Personally I'm not worrying about it.

 

[autorouter]

I think the main problem is that lithium batteries don't take kindly to being overcharged. Unlike lead-acid-based batteries that need to be taken to 100% full every month or so to clear out any residual sulfation. It's very difficult to be sure that when you're trying to charge to the full 100% that you don't do any overcharging, especially if you are charging at a fast rate. I think it's best to stick to 90 to 95%. So if you want 200Ah, then get a 220Ah battery and charge it to 90%

 

[Guigsy]

I think the main problem is that lithium batteries don't take kindly to being overcharged. Unlike lead-acid-based batteries that need to be taken to 100% full every month or so to clear out any residual sulfation. It's very difficult to be sure that when you're trying to charge to the full 100% that you don't do any overcharging, especially if you are charging at a fast rate. I think it's best to stick to 90 to 95%. So if you want 200Ah, then get a 220Ah battery and charge it to 90%

For LiPO4 chemistry, the effect exists, but my understanding is the reduction in life is pretty minimal.

It's also very hard to manage your batteries so they top off at 95%. Ideally, you'd be able to tell the BMS to block charging, but I've not seen one that can do that yet.

As far as I'm concerned, there's bigger stuff to worry about than babying your batteries.

 

[the1andonly]

For LiPO4 chemistry, the effect exists, but my understanding is the reduction in life is pretty minimal.

The question is still what is it?

It's also very hard to manage your batteries so they top off at 95%. Ideally, you'd be able to tell the BMS to block charging, but I've not seen one that can do that yet.

It is relatively easy. I use the bmv712 to switch the relay based on SOC, the relay controls a 12V 30A ssr to switch the input or output of solar controller. I use one to control the input on one votronics mppt (no solar in) and another on a second votronics duo mppt that allows a trickle charge to SB wilst LB is off. On the victron ap i have 3 files for different levels of SOC 60, 90, 100% Winter, summer, i need it now.(or whatever suits you).

As far as I'm concerned, there's bigger stuff to worry about than babying your batteries.

A few years ago it was being bandied about as a real issue and best way to winterize was to issolate the negative terminal. But probably there are bigger things.

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[LithiumConvert]

I am with Guigsy, et al. There are more important things to worry about.

If my batteries only last 9 (or even 8) years instead of 10, I willl be more than happy.

 

[the1andonly]

The question is still what is it?

 

[Tombola]

Mine is a "grab bag" and I grabbed it 7 hours ago in murcia and I'm now in zaragoza, I started with 100% of 400ah. which it has been sat at for 3 weeks pretty much ....thanks to the sun..

I don't worry about it.

They say Sat "holding" a charge, so they never say what drain it should have. Mine drip drains a battery master to keep the cab topped up, ad the small USB lights in the hab area 1 amp a day ? ....is that enough..who knows who cares...
Enjoy it

 

[Cush]

The question is still what is it?

Do you mean “what is the damage caused by sitting at 100%?”

 

[Bessy765]

We have 700 watts of solar a Victron 12/2000/80 inverter charger and 2 x 100 amp Transporter Lithium Batteries. The installer stated a B2B is not required the installation is warranted for 5 years the batteries for 10. When not in use the motorhome is kept in our garage so no benefit from soar the tracker and monitoring systems run the batteries down so when it gets to 70% I switch on the charger until they are at 95%. When as now we are in France the van is parked up in our holiday cottage garden and the solar keeps it at or around 100% so far in just over 4 years this is how our van is used so 23300 miles later all is well. Quite happy for the batteries to cope with how we are using them, how cold the beer is is to me more important.

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[the1andonly]

Do you mean “what is the damage caused by sitting at 100%?”

put simply yes. or the real question what is the effect of "normal use" and running normal charge methods to maintain 100%, not just charged to 100% and left disconected. In a UK summer my battery can be at 100% by 9:30am

 

[Raul]

There is a Australian outfit, that started the test 10-12 years ago with various batteries, incuding Pylontech, BYD, sympliphy, Rolls, LG chem, even gen 1 tesla later on, red flow, and many more. They simply charged/ discharged to the limits of manufacturer, fully 100%, and indeed there is degradation. Some more than others. And, some manufacturers pulled the battery from the test due to fails, Aquion was first one. They just finished and concluded the test late last year. Few years back, I used to log in and watch life data, as it was done. There was some fails, some replacements and more fails, and some did very well indeed. All lost over 20% capacity, others more, over 8 or so years completed tests, all charged to 100%. I remember Pylontech did very well, given that was the cheapest LFP in its class, and ppl was weary at the time.
There is tons of data and papers out there, and its much better understood than 10-12 years ago. LFP its NOT a new tech, its been in the market for around 20 years now. Remember the old victron blue boxes with a wire sticking out? There used to be 4 yelow thundersky/ later winston prismatic cells inside. Yanks used Calb and A123 systems for ages.
I know personally of at least two cases, with LFP since 2014, one with sinopoly and one with winston. All serving off grid dwellings. At the time lfp was very expensive and not many importers. So the data was not so available and ppl played it conservatively, due to cost.
One thing for certain I can tell you, charge to 3.45V and 0.3C max, gives about 1-5% degradation in 10 years. There are other factors involved, not just high voltage, high temp >35C is number one killer.

Try " battery university " site, for an insight of LFP, even Wikipedia is dated.

 

[Cush]

put simply yes. or the real question what is the effect of "normal use" and running normal charge methods to maintain 100%, not just charged to 100% and left disconected. In a UK summer my battery can be at 100% by 9:30am

I would reckon that although it’s at 100% there will still be energy in and energy out due to your use. That doesn’t feel the same as left static at 100%.

My very very basic understanding is that it’s the over charging, perhaps in search of 100% that can be life limiting (dendrites, short circuits and perhaps in very worst scenarios, releasing the electrolyte). With the battery voltage being all the individual cells totaled, the battery can keep charging to reach the predetermined 14 or whatever volts even though one of the cells is maxing out already and being over charged. Thanks goodness for a bms. More than happy to have my understanding corrected.

 

[Raul]

I would reckon that although it’s at 100% there will still be energy in and energy out due to your use. That doesn’t feel the same as left static at 100%.

My very very basic understanding is that it’s the over charging, perhaps in search of 100% that can be life limiting (dendrites, short circuits and perhaps in very worst scenarios, releasing the electrolyte). With the battery voltage being all the individual cells totaled, the battery can keep charging to reach the predetermined 14 or whatever volts even though one of the cells is maxing out already and being over charged. Thanks goodness for a bms. More than happy to have my understanding corrected.

Dendrites not so much with lfp, lithium plating yes, irreversible capacity loss if you charge at low temps under zeroC. That,s because the electrolyte becomes poor carrier under low temperature. When fully charged the lithium is all on one side of the separator, the higher the voltage the more under pressure. The longer is kept at that condition, the more degradation will occur. Same goes for the other end, when fully discharged, it will never come back, hence we still need to keep 2.5v each cell, for it to come back. When a battery is half charged, 50/50 each side of separator, can go in storage for years, as there is no stress from neither side, as long as you replace the self discharge.

On another note, I have several DeWalt power tool batteries, li ion, they get a hard ish life, (grinder, circular saw etc.) I number them and keep track of their use. At about 10 year plus, the discharge is much weaker, and 2/3 capacity left or less. IF li ion can las that long, lfp should easily do double if not abused.

 

[Clive Mott]

A couple of fasets here. A charging algorythm for a LiFePo4 battery is typically constant current up to 14.4 or 14.6 volts (both figures have be given by different outlets but 14.4 gives a longer battery life) and then turn off the charger. In most cases there is a fallback voltage typically 13.5 volts or 13.8 volts quoted. However the concerns associated with %charge during storage are normally associated with a different lithium technology, that used in your leccy bike or scooter. Guidance for these is to store or transport then when the state if charge is not much more than 50%. The reason is stability, they are less likely to catch fire when only half charged. Dont forget there is now at least one fire every day in the UK associated with lithium ion bike and scooter batteries and nearly all take place when they are on charge. That is why we no longer charge ours in the moho garage. But could not do without them!! Short extension lead comes in handy.

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[wfdTamar]

It's also very hard to manage your batteries so they top off at 95%. Ideally, you'd be able to tell the BMS to block charging, but I've not seen one that can do that yet.

If you get the app for your BMS, it's all in there. You can set a voltage at which charging stops. Or there might be a setting in your chargers. It's easier to think in terms of voltage regarding harm caused by charging all the way. This bloke does endless experiments about all this stuff. He's decided to stop charging at 3.40-3.45 volts per cell (so 13.6 to 13.8 volts) because to get the rest (to 3.65 volts or 14.6 is so little extra Ah over such a long time and that's where the harm to life is done.

https://www.youtube.com/@OffGridGarageAustralia

 

[Guigsy]

If you get the app for your BMS, it's all in there. You can set a voltage at which charging stops. Or there might be a setting in your chargers. It's easier to think in terms of voltage regarding harm caused by charging all the way. This bloke does endless experiments about all this stuff. He's decided to stop charging at 3.40-3.45 volts per cell (so 13.6 to 13.8 volts) because to get the rest (to 3.65 volts or 14.6 is so little extra Ah over such a long time and that's where the harm to life is done.

https://www.youtube.com/@OffGridGarageAustralia

Does it make any logical sense to do it though? I can voluntary not use 5% capacity for the next 10 years. Or I can use all 100%, but after 10 years, I'll have lost 5%...?

 

[two]

I have my laptop on charge all the time. It's a different kind of Lithium, I expect, but is still working 6 yrs later. The capacity is very much reduced, however. It might last an hour now, rather than the several when new. Whether the drop in capacity has been increased because of the continuous charge or not, I've no idea. I expect much of the reduction to be unavoidable aging,
When the thing's of little use, I'll get another.

 

[Guigsy]

I have my laptop on charge all the time. It's a different kind of Lithium, I expect, but is still working 6 yrs later. The capacity is very much reduced, however. It might last an hour now, rather than the several when new. Whether the drop in capacity has been increased because of the continuous charge or not, I've no idea. I expect much of the reduction to be unavoidable aging,
When the thing's of little use, I'll get another.

Yes, different lithium ion battery chemistry. My most recent laptop had an app that had the option to assume it was plugged in all the time and to keep the battery at a lower state of charge to make the battery last longer.

The Lithium Iron Phosphate chemistry used in hab batteries does lots more cycles than the Lithium Cobalt that's often used in laptops and phones. And it doesn't mind being fully charged as much.

 

[Smokaijo]

This is probably a different Lithium battery under my electric power chair but from experience charging my first lot to full every day shortened their life capacity - whereas with the new ones I have to give them a full 12 hour charge but only when they reach 20% capacity and only for the first 2 charges then after that as and when.
So if I know I’m at home pottering I don’t charge them until they reach 20% but if I know I’m going out for the day I charge them until they reach 100% ( or green light on my charger ) then they are good to go.

Like I said they may not be same as moho but I think that keeping them at full in my experience all the time does damage them

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