Leisure battery help

J

JumpShip

Senior Member
T6 Legend
Firstly this isn't in our vdub , it's in our motorhome , secondly I must confess to knowing very little about leisure batteries and associated electrickery.
Our van has been in storage for the last 8 weeks and i thought I'd go over to give it a wash and a check over before it's upcoming mot.
Plugged it in to the HU and cracked on scrubbing the exterior , left it over night and returned the following day to continue with the inside .
Opened the door and got a strong whiff of eggyness (wasn't there previously).
The van has 2 leisure batteries (that have just been health checked) and it was here the stink appeared to be coming from .
One of the batteries felt cool to the touch , the other very warm .
I assume the warm one isn't a happy battery ? Would this be correct ?

Details of the system and how it's wired are very thin on the ground , all I know is it has 2 AGM batteries, 2 smallish solar panels on the roof and I assume a mains charger which looks after levels whilst on EHU .
I have a meter inside that tells me what the batts are currently at (combined not individually) and that's my only way of monitoring them .

What should I do next ?

Any help much appreciated.

P.s. I have no plans to rip the lot out and replace it all with lithium at the mo.
 
JumpShip said:
Firstly this isn't in our vdub , it's in our motorhome , secondly I must confess to knowing very little about leisure batteries and associated electrickery.
Our van has been in storage for the last 8 weeks and i thought I'd go over to give it a wash and a check over before it's upcoming mot.
Plugged it in to the HU and cracked on scrubbing the exterior , left it over night and returned the following day to continue with the inside .
Opened the door and got a strong whiff of eggyness (wasn't there previously).
The van has 2 leisure batteries (that have just been health checked) and it was here the stink appeared to be coming from .
One of the batteries felt cool to the touch , the other very warm .
I assume the warm one isn't a happy battery ? Would this be correct ?

Details of the system and how it's wired are very thin on the ground , all I know is it has 2 AGM batteries, 2 smallish solar panels on the roof and I assume a mains charger which looks after levels whilst on EHU .
I have a meter inside that tells me what the batts are currently at (combined not individually) and that's my only way of monitoring them .

What should I do next ?

Any help much appreciated.

P.s. I have no plans to rip the lot out and replace it all with lithium at the mo.
Click to expand...
Don't breathe the gas!
Switch off the EHU.
Wait for @roadtripper to advise you.
Consider ripping out the AGM's and replace with lovely Lithium!
 
Sounds like the charger has boiled one battery dry. Most MH just have a dumb 13.5v power supplys, and not a smart chargers. (Which can boil dry poorly SLA battery's). Also some AGM battery s don't have the external vent tube, which is why it vented inside the van.

It would be best to replace both batterys with new AGMs, and look at upgrading the power supply with a 12v smart charger.

Also look at the lithium battery's too as an upgrade option.
 
The smell is the battery venting, if not done already turn everything off and disconnect both batteries.

If a battery has got hot enough to vent then consider having the system checked by an auto electrician - we can advise on the forum but someone physically present checking the system is better placed to see what damage may have been done.

I'm assuming if you have 2 they are wired together as a bank?

The most likely cause is that they are no longer identical. As a lead acid battery fails in a bank it's voltage will fall so it will draw energy from the good batteries to try and charge itself, as the interconnects are usually very high current the current draw can get to be substantial and the battery will overheat.

I've had a 7Ah SLA UPS battery pack that did this to me and led to the failing battery getting so hot it melted the plastic case.

If you are not upgrading to LiFePo then you'll need to replace both batteries with identically matches ones, they can then form as a bank rather than a single battery. I'd also second @Dellmassive suggestion that if you have an "all in one" style PDU system with a fixed voltage PSU rather than a charger you upgrade it to a decent smart charger, you'll get more life out of your next set of batteries and pay for it from that saving.

When running a bank be especially careful to stick to the 50% discharge rule, it's under deep discharge that the small differences.between individual batteries can be more significant.
 
Thanks guys , that's kind of what I had in my head but as mentioned I really don't know anything about what kit is in there or what I'm doing really .
I'll get a load of pictures up . :thumbsup:

Sounds like an expensive month :rolleyes:
 
They don't look like they are linked together to me - I would expect to see hefty cabling between each terminal across the top.
 
There is only 3 pieces of thin little cabling on the positive on the right hand battery, I would expect to see 100 - 150Amp cabling joining them or copper bars. Also needed on the negatives. I have 180 Amp cabling joining my two 110Ah batteries for example.
As I said - hefty cabling.
 
That looks awfully like someone who didn't understand leisure battery system added an extra battery to try and improve storage, probably from the Halfords parts bin...

Out of interest is it the Lucas non AGM battery that's getting hot?
 
If the yellow crimp terminals highlighted in purple are the wires connecting the two batteries then, to be frank, those are dangerously undersized.


20250225_132951.jpg


A lead acid battery can supply several hundred amps of current and those don't look like they'd take more than 15 amps at best.

You have batteries with unequal chemistry so different resting voltages so current is always going to try and flow between them.

Given you already have noticed heating due to this if it continues to get worse there is a strong chance those wires could overheat to the point of a fire.

I really urge you to find a local auto electrician and I would recommend disconnecting at least the secondary battery completely until you work out what's going on.
 
Yes the yellow connector circled is the wire linking the negs on the batterys.
Googled the number on the lucas and it says 104ah AGM ....its actually the other battery that's getting hot .
Drove it to the mot station this morning and it was stinking by the time I got back (but still cold)
We bought the van 2nd hand with one 'careful' owner :rolleyes: ..
The van was hab checked 8 weeks ago (including batteries) and given a clean bill of health ...also he must have forgotten to mention how pants the install was .
 
As you have found - a habitation check isn't worth the paper that it is written on! They originate from caravan checks and don't apply to modern vans and equipment, well at least those done by non-specialist surveyors don't.
Why didn't you disconnect the leisures before driving as you knew that there was a problem with them?
Strange that the Lucas battery isn't marked as AGM.
 
Brain was mush smorn, been up half the night and never gave it a thought before I left .

Strange that the dealers that removed good money from my bank account when we bought it never mentioned either that it wasn't suitably installed.
I need to look at removing that mess and what I buy to replace it all .
 
JumpShip said:
Shame Drive Wayne sold that big beast of a lithium battery just a few weeks back :rolleyes:
Click to expand...
You shouldn't need anything as big as that, a nice 100Ah lithium will give you more usable 'credit' than your old pair, and will give you room to have a small snooker table in the space! But, too much power is never a bad thing!
 
It's more the charging side of things that scares me a little about the change over to lithium .
The m/h isn't ever used on anything but ehu so it doesn't need massive capacity i suppose.
The extra expense that I could live without at the mo and the timescale as I need it at the weekend :rolleyes:.
And of course it's lashing it down this morning and I want to crack on .
 
If you are mostly needing the leisure system to be an occasional off grid backup when travelling or stopping over and will mainly be in EHU then there are less reasons to go LiFePo - with an all in one system such as yours you'd be looking at a new mains charger, DC-DC charger and solar charger (I suspect the simple controller you have is not lithium suitable) as well as the battery.

Your best path now is to sort out the wiring and consolidate it on to one battery, and replace that with a good branded battery. That shouldn't be too much cost, yes you'll have limited run time and the life may be as low as 2-3 years but it would be a good fit for the use you say you will put it to.

I strongly suspect you just have a basic split charge system so find out what your main vehicle battery is (AGM or Standard Flooded) and fit the same chemistry type. Yes they will be in a bank when the engine is running but not at rest so there is less concern, so long as they are the same charging voltage.

But, seriously, stop using the system and make it safe. If the batteries are getting hot enough to vent so you can smell them, and they look like modern maintenance free so they will only be venting at emergency pressures, you are taking a heck of a risk.
 
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