Cause of leisure battery overheating?

Joff and Gill replied on 03/07/2023 13:54

Joff and Gill

Posted on 03/07/2023 13:54

Upon leaving site last Saturday, when I opened the leisure battery compartment on my caravan to disconnect the hook-up cable (following the correct procedure), I realised that the battery was extremely hot. It wasn't smelly or bulging but as it was so hot, I worried about it exploding and so disconnected it putting it somewhere that it could cool down. As I disconnected the hook-up power, the caravan meter dropped from 13v to 10.5 v. Once home 6 hours later, the battery was still slightly warm and the voltage (using my multi-meter) was only 5.5v so I know I need to replace the battery. However I don't know if it overheated because:

The battery (which is at least 4.5 years old) has just died of old age
The battery has been overcharged by the charger (between the hook-up input and the battery)
The battery has been overcharged by the solar panel (via the panel controller (CMP12))
Something else

I've had no other battery/electrical problems with the same set-up since buying the caravan 4.5 years ago.

Given the urgency of the situation on site (& my ignorance about the order of disconnecting/connecting solar panel controllers), I didn't disconnect the solar panel from its CMP12 controller until today (Monday).

I reconnected my hook-up lead at home (with battery disconnected) and measured the voltage across the leads that come from the charger - 13.5v (which seems ok). I don't know if it was useful to measure the current with battery disconnected but it was 0.5mA. This leads me to think that option 2 isn't the problem.

After disconnecting the solar panel from its CMP12 controller today, the panel (in sunshine) measured 21.5 volts across the solar panel connections (in fact it measured the same when the panel and CMP12 were connected). I measured 0.82A across the solar panel connections.

With the solar panel connected to the CMP12 panel controller (but with the battery still not connected to anything), the output from the controller to the battery leads is the same as the input to the controller (i.e 21.5v 0.82A). I'm wondering if the CMP12 is now broken (either because it was anyway and thus overcharged the battery, or because I disconnected the battery from the controller before disconnecting the solar panel?

I clearly need a new battery but don't want to break that one by overcharging it.

Any advice gratefully received. Thanks in anticipation

13 replies

dave the rave replied on 03/07/2023 20:47

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dave the rave

Posted on 03/07/2023 20:47

Sounds as if your battery has failed,places like halfords can check it for you and supply a replacement if necessary and at the age of your battery I would expect the battery to be the problem but the onboard charger could be faulty!

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replied on 03/07/2023 21:04

Posted on 03/07/2023 21:04

The user and all related content has been Deleted User

mickysf replied on 03/07/2023 21:19

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mickysf

Motorhomer from South Humberside

Posted on 03/07/2023 21:19

Sounds like possibly just one cell, maybe two have failed rather than all. That could cause the charging system to perform incorrectly.

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Joff and Gill replied on 03/07/2023 22:54

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Joff and Gill

Caravanner

Posted on 03/07/2023 21:04 by

You don't say whether or not your charger is a smart charger n give its make and model. Nor do you give the make, size, and type of your battery.

Posted on 03/07/2023 22:54

Thanks for taking the time to reply Dave,

I had planned to take the battery to Halfords today but got waylaid. That's tomorrow's task. As I mentioned I'm pretty much convinced the battery is dead - the question is "why?" (and I'd like to know that so that I don't ruin the replacement battery)

Joff and Gill replied on 03/07/2023 23:06

Member

Joff and Gill

Caravanner

Posted on 03/07/2023 21:04 by

You don't say whether or not your charger is a smart charger n give its make and model. Nor do you give the make, size, and type of your battery.

Posted on 03/07/2023 23:06

Thanks Dorset Dave

Re the charger, the answer is "I don't know", sorry. Its a 2012 Bailey Pegasus Rimini II caravan that I bought 2nd hand 4.5 years ago. I can't find anything in the manual and despite trying to trace the cables, they disappear behind units that I'm loathe to pull apart. I'd hoped that mentioning there's 13.5v from the charger output (with battery disconnected) might give a clue.

I've attached a photo of the top of the Hanhook battery that got very hot. There's no other information on the sides of the battery that I can see

Gallery

Joff and Gill replied on 03/07/2023 23:08

Member

Joff and Gill

Caravanner

Posted on 03/07/2023 20:47 by dave the rave

Sounds as if your battery has failed,places like halfords can check it for you and supply a replacement if necessary and at the age of your battery I would expect the battery to be the problem but the onboard charger could be faulty!

Posted on 03/07/2023 23:08

Sorry Dave - I managed to send my reply to your input to [Deleted User User] - its been one of those days!

Joff and Gill replied on 03/07/2023 23:13

Member

Joff and Gill

Caravanner

Posted on 03/07/2023 21:19 by mickysf

Sounds like possibly just one cell, maybe two have failed rather than all. That could cause the charging system to perform incorrectly.

Posted on 03/07/2023 23:13

Thanks Mickysf,

I guess that's my conundrum i.e. I don't know if some cells died of 'natural causes' which then led to the others being overcharged (& getting very hot), or if something else (e.g the caravan charger or the solar panel controller) caused those cells to fail

From the photo of the battery that I've now added, the battery condition indication supports the battery needing to be replaced

replied on 04/07/2023 08:00

Posted on 03/07/2023 23:06 by Joff and Gill

Thanks Dorset Dave

Re the charger, the answer is "I don't know", sorry. Its a 2012 Bailey Pegasus Rimini II caravan that I bought 2nd hand 4.5 years ago. I can't find anything in the manual and despite trying to trace the cables, they disappear behind units that I'm loathe to pull apart. I'd hoped that mentioning there's 13.5v from the charger output (with battery disconnected) might give a clue.

I've attached a photo of the top of the Hanhook battery that got very hot. There's no other information on the sides of the battery that I can see

Posted on 04/07/2023 08:00

The user and all related content has been Deleted User

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Joff and Gill replied on 04/07/2023 08:26

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Joff and Gill

Caravanner

Posted on 04/07/2023 08:00 by

The problem is that many older caravans are equipped with dumb chargers. Unlike smart chargers they provide a constant amperage and voltage regardless of the needs of the battery and can over charge (cook) it. I suspect that is what has happened to yours.

In your position I would get a replacement open rather than sealed lead acid battery (the old type with individual screw in plugs for each cell) and keep an eye on it whilst the charger is on. With a dumb charger you have to do the management rather than the computer. Alternatively you could replace your charger with a smart charger such as a CTEK.

Tayna Batteries are a reliable supplier and very helpful if you phone for advice, they also sell a limited range of CTEK chargers. Yours is a sealed group 31 battery if you want to replace like for like.

Posted on 04/07/2023 08:26

Thanks very much [Deleted User User]. That makes sense. I'll give Tanya Batteries a call

Is it also possible that the solar panel (via its controller) has overcharged the battery? The fact that with the solar panel connected to the CMP12 panel controller (but with the battery still not connected to anything), the output from the controller to the battery leads is the same as the input to the controller from the solar panel(i.e 21.5v 0.82A).

Joff and Gill replied on 04/07/2023 14:20

Member

Joff and Gill

Caravanner

Posted on 04/07/2023 14:20

Sadly, Tanya Batteries felt unable to advise (apart from which battery to buy).However, I managed to find the charger this morning (please see 1st photo). It looks to be part of the unit that contains the breakers, RCD etc. I found it by tracing the thick orange cable (from the 3 pin EHU input socket) and the black cable (which contains both a positive and a negative thinner cable that connect to the battery terminals) to where the charger is under the front seat. The next photo shows these cables from the rear of the battery compartment inside the caravan (the thick grey cable connects the positive battery terminal to the motor mover isolation switch)

The black cable in the 2nd photo is the one where I measured 13.5v across its +ve and -ve wires when the EHU cable was connected. Does anyone know if this cable is used both for charging the battery when the EHU is connected, and for 12v supply from the battery when the EHU isn't connected?

The only other wires connected to the battery (when installed) are the thin black and red ones (next to the thick blue cable) in the 3rd photo. These comes from the output side of the solar panel controller shown in that photo