Adding a second leisure battery

ToBoldlyGo

ToBoldlyGo

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i have an older motorhome. The battery locker has a single 85ah battery and it's full.
I have a 175 watt solar charging the leisure battery only. Sargent tell me that my
charger is only designed for a wet battery (not agm/gel).

Plan: replace the battery locker battery with as big a one as will fit (100ah say)and connect a
second twin 100ah battery. I don't know about electrics, I've heard of hydrogen. I think
I want a battery box to house the second battery, and the battery box will be connected
to the first battery, and somehow vent the gas. The battery locker lid has a hole in it and
a fuse is mounted outside the locker. Doing this is outside my competence, but out of interest,
am I right in thinking battery box and if so how will the electrical connection
be made, will an extra hole have to be made in the lid? I assume there will be an extra hole
in the lid to vent the gas from the battery box? Why don't wet car batteries have ventilation tubes
connected, is it because there is a lot of airflow under a bonnet?

Any recommendations please for some to do this in Brighton (or 10 mile radius) area?
 
ToBoldlyGo said:
i have an older motorhome. The battery locker has a single 85ah battery and it's full.
I have a 175 watt solar charging the leisure battery only. Sargent tell me that my
charger is only designed for a wet battery (not agm/gel).

Plan: replace the battery locker battery with as big a one as will fit (100ah say)and connect a
second twin 100ah battery. I don't know about electrics, I've heard of hydrogen. I think
I want a battery box to house the second battery, and the battery box will be connected
to the first battery, and somehow vent the gas. The battery locker lid has a hole in it and
a fuse is mounted outside the locker. Doing this is outside my competence, but out of interest,
am I right in thinking battery box and if so how will the electrical connection
be made, will an extra hole have to be made in the lid? I assume there will be an extra hole
in the lid to vent the gas from the battery box? Why don't wet car batteries have ventilation tubes
connected, is it because there is a lot of airflow under a bonnet?

Any recommendations please for some to do this in Brighton (or 10 mile radius) area?
Click to expand...

The battery box does not have to be sealed the way a gas locker is sealed. BUT the batteries do need a vent pipe out of the batteries to outside the MH, usually under the chassis.

Our three lead acid batteries are located under the seats and are certainly not sealed in any way to prevent air circulating from them to the cab / hab. But they do have a vent pipe on each one.
 
Thanks. The battery locker is under the floor of one of the bench seats in the lounge. The locker has a large, 2" by 2" say opening where the pipe runs from the battery to the outside. I envisage the additional battery being placed next to the lid of the locker, ie the first battery will be in the extant locker, and the second battery will be above it and to the side. How do the tubes from your 3 batteries connect to the outside?
 
Instead of venting through the lid they can exit through the battery box floor.
A small hole just big enough for the vent tube then sealed around the tube from outside.
Much neater and easy access to the battery.
 
The problem I'm trying to fix is that my solar 175w is too much for the single wet battery, eg in the sunny days recently the solar's not doing anything because there's nowhere for the energy to go. I like the idea of just adding a single extra wet battery because my sargent charger will still work when on ehu. Another possibility just occured to me to avoid venting problems which is to replace the wet battery with lithium if that just means changing a setting on the victron solar controller, I'll have to check. If I went that route what would I need as a backup mains charger?

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Buy an appropriate charger and turn off your onboard charger (or pull it's fuse).
Two matched batteries joined red to red and black to black will behave like one big battery. Add a Battery Master and surplus charge goes to engine battery)just two small wires).
 
Firstly the Sargent charger is limited to one battery mostly due to it's charging rate. If its anything like mine (in a 2019 built van) max output was 12A at 13.8V. That would take hours to recharge a 100Ah battery, and that was whether from engine or hook up. Worse it was a flat rate 13.8V, no absorption or float so even lead acid batteries couldn't be charged properly.

But, if you are on hook up, if it takes hours to recharge is that a problem, even if you have two batteries so it takes even longer. Concern may be heat in the charger when many are fitted in enclosed cupboards. But still not good for batteries without their own management systems, such as lithium with a BMS built in, that can protect against overcharge / wrong charge.

Don't overfret that on a good day the solar has done its job and fully recharged so some then goes to waste. On a cloudy or autumn day you have less charge from the solar. What you do want, and currently seem to have, is enough solar to recharge your average use.

Reason for changing or extra battery is that you need and would use the capacity. So if you take your current battery down to 50% regularly you need more battery, or if you have heavy discharge such as large inverter. If you don't do that then why spend out? Remember leas acid /AGM batteries generally only 50% of total is usable, Gel are more tolerant but take longer to properly recharge, lithium can do high loads and fast recharge down to almost empty.

If you need more battery, but no space, then, as I found, lithium whilst expensive becomes the answer. Same physical size as lead acid will more than double your usable capacity. Some are sold as drop in solutions, although to work best your Sargent charger on engine would be isolated and a B2B direct DC to DC charger fitted instead. But if you already have Victron Solar, change its profile to lithium and you solve most issues that the battery wouldn't ever be charged correctly even if you rely on the Sargent. I also mostly disable the Sargent EHU charger (fuse pulled), so if on hook up things like fridge run on mains whilst lights remain on 12V via battery that is more than recharged by solar.
 
ToBoldlyGo said:
I don't know about electrics, I've heard of hydrogen. I think
I want a battery box to house the second battery, and the battery box will be connected
to the first battery, and somehow vent the gas.
Click to expand...
I think you need to know a bit more about modern batteries. Pure lead is too soft and flexible to make the plates in a battery, so it is alloyed with other metals to make it stronger and stiffer. The old lead-acids were made with lead-antimony alloy, and needed vents in each cell and a screw cap to allow topping up with water, because they produced gases all the time while charging and discharging.

Then they discovered that the gassing was caused by the antimony, so they changed to lead-calcium alloy, sometimes with a bit of silver too. This stopped any gassing from the normal charge/discharge cycle. The batteries could be sealed, with a pressure release valve and a small vent tube attached in case of a major fault. And no need to top up any more. This was discovered over 70 years ago, but for some reason is still described as an innovation.

You can still buy the old lead-antimony batteries, because they are a bit cheaper and are often used in well-ventilated environments anyway. But in a motorhome you should use a sealed lead-calcium battery and a vent tube to the outside. Or you could go for a Gel or AGM battery that also is sealed with a pressure valve and vent tube.
 
Thanks very much everyone. The below, just for interest, is what Sargent said to me when I wrote them some months ago when thinking of adding additional wet batteries.

But what I am thinking of now is (thanks kannon fodda):

just swap out the wet 75ah platinum battery for, I'm guessing on physical size here, a single 100ah lithium. The victron solar charge controller will just I think need the config change kf mentioned. The sargent control panel allows me to choose if the sargent will charge the wet leisure or wet vehicle battery so I will simply remember to keep it set to the vehicle battery always. I don't understand the comment about isolating the sargent. I assume the vehicle battery side of things will still work? If I forget and try and charge the leisiure battery then the lithium battery BMS will protect itself? For days when there's no solar output and I'm on ehu I'll still need a charger of some sort?

-What you do want, and currently seem to have, is enough solar to recharge your average use.

I guess we quite often are not on hookup, at aires, we use aires a lot more now we have solar and a refillable gas tank. I do fret you guessed it, at having a big solar panel and the energy 'going to waste'! :-). The only larger consumption from the battery is I expect to use our microwave 1000watts for may be 20 minutes a week.

--

Your Tribute will have the EC155/175/176 system. They all have a fixed voltage 13.8V charger. This is often deemed too low by AGM manufacturers - please seek advice from the manufacturer of the battery based on this charge voltage.
We also generally recommend a max of around 110Ah capacity for the charger you have fitted; people often fit more (fairly often double this) which results in slower charge times and as the charger is working harder, may also adversely affect it's long time life.
When connecting batteries in parallel, it's important that the batteries are the same age, brand and type as they have to work as one battery. If the batteries perform slightly differently, overall performance/capacity can be affected. For this reason, I normally advise not to connect more than two of the same batteries in parallel (consider a 'change over switch' or the like for more).
All our units have a charger isolator switch - an external suitable charger can be retro fitted by a professional and the internal charger switched off.

I hope this helps.
 
ToBoldlyGo said:
For days when there's no solar output and I'm on ehu I'll still need a charger of some sort?
Click to expand...
I have a Victron charger for my 100Ah sealed lead-acid leisure battery. Victron do various versions, with various amp ratings. The main difference is the case - the 'IP22' versions need to be installed in a dry place, but the 'IP65' versions are splash-proof.

I have an IP65 15A charger. It is a quality charger, and doesn't have the problem that Sargent mentioned about long-term reliability if worked hard. It has several charge profiles including lead-acid, Gel, AGM and lithium. It also has a 'Power Supply mode', which can be used if no battery is present. Many other chargers won't give out any power if there is no battery present.

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Last edited:
Jev88 said:
Buy an appropriate charger and turn off your onboard charger (or pull it's fuse).
Two matched batteries joined red to red and black to black will behave like one big battery. Add a Battery Master and surplus charge goes to engine battery)just two small wires).
Click to expand...
There are right and wrong ways to connect up 2 batteries

connecting-two-batteries-in-parallel.jpg
 
I still need recommendations please for someone local to fit the new battery and equipment.
 
If I physically put some tape or something over the Sargent battery charger switch to remind me to stop using that, to upgrade my single wet battery to a lithium, is it as easy as physical swap of the batteries (same connection posts?) and change my victron config?

I should of course still have some ability to charge the lithium when on ehu but as I don't know how to do that bit.

My focus now is really on finding someone nearest in Sussex who loves electrics, but sunstore I find difficult to communicate with (like the company, they did my refillable gas and
solar install think they're just too busy), vehicle electrician recommended by my car garage cannot accommodate 3 metre mhome and no joy with mcea yet either.

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Last edited:
ToBoldlyGo said:
If I physically put some tape or something over the Sargent battery charger switch to remind me to stop using that,
Click to expand...
There's no need to stop using that charger if it's the only mains charger in the system. We are used to the idea that if we hookup to the mains and leave the charger on, the leisure battery will eventually get up to 100% charge, ready for when we move on to a possibly off-grid stop. With that charger and a lithium battery it will only charge up to a fraction of the total, maybe 50%, no matter how long you leave it. The solar will continue topping it up if it's sunny. But 50% is better than nothing ig the weather is against you.
 
I'm now thinking of replacing the wet battery with one of these lithiums:

Lithium Battery,Leisure Battery,Solar Panel Battery|Renogy UK

Lithium batteries have a longer life cycle compared to AGM and GEL batteries. The 12 volt batteries are the solar batteries most cost effective.
uk.renogy.com uk.renogy.com

Thanks autorouter. I see that I will be able to use the Sargent to charge when on ehu. The last part I need to understand is the alternator, oh and what adaptors do I need for the lithium battery connections to fit into the wet battery connector? To check if the alternator charges my leisure battery, which may well be full from the solar, connect multimeter to battery posts then have someone start engine and see if voltage changes even briefly?
 
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