Caravan battery "boiling"

[DaveG]

Question is about my caravan battery but the basic principles are (I guess) the same as for a car battery.

Brought the van down to the house to prepare it for hols. This included connecting the van to the mains and putting the battery on charge thru' the on-board charger. (Yes I know I should have taken the battery out and maintained its charge over the winter but I didn't)
The battery has been on what should have been a trickle charge for around 4 weeks now. Acrid smell appeared yesterday and it seems the battery has been boiling.

I am assuming that the charger is at fault but before I go down that line is there any way that a problem with the battery itself failing would cause it to boil.

Thanks,
Dave

[ANDY W]

I have seen a battery sort of boil before and that was down to rapid charging or charging with a very high ampage. Maybe the charger is to blame but I dont really know.

[neilrj]

Question is about my caravan battery but the basic principles are (I guess) the same as for a car battery.

Brought the van down to the house to prepare it for hols. This included connecting the van to the mains and putting the battery on charge thru' the on-board charger. (Yes I know I should have taken the battery out and maintained its charge over the winter but I didn't)
The battery has been on what should have been a trickle charge for around 4 weeks now. Acrid smell appeared yesterday and it seems the battery has been boiling.

I am assuming that the charger is at fault but before I go down that line is there any way that a problem with the battery itself failing would cause it to boil.

Thanks,
Dave

Hi Dave

Unless the battery was low on electrolyte to start with most van chargers (actually just power supplies at 13.8V, so not quite chargers!)
shouldn't ever boil a battery or even actually charge it too much.
How old is the van and battery and is the battery a 'maintenance free' or something a bit older with cell caps etc.

neilrj

[DaveG]

Hi Dave

Unless the battery was low on electrolyte to start with most van chargers (actually just power supplies at 13.8V, so not quite chargers!)
shouldn't ever boil a battery or even actually charge it too much.
How old is the van and battery and is the battery a 'maintenance free' or something a bit older with cell caps etc.

neilrj

Battery is a sealed unit and the van is just over 2 years old.
dave

[davree]

Question is about my caravan battery but the basic principles are (I guess) the same as for a car battery.

Brought the van down to the house to prepare it for hols. This included connecting the van to the mains and putting the battery on charge thru' the on-board charger. (Yes I know I should have taken the battery out and maintained its charge over the winter but I didn't)
The battery has been on what should have been a trickle charge for around 4 weeks now. Acrid smell appeared yesterday and it seems the battery has been boiling.

I am assuming that the charger is at fault but before I go down that line is there any way that a problem with the battery itself failing would cause it to boil.

Thanks,
Dave

I have no experience with caravans so appologise if I am mistaken but even for a trickle charge isnt 4 weeks a bit long for any type of battery to be on constant charge for??!!

Could it be that it has been cooked/overheated due to being on charge for such a long time??

Edit: OK just done a search on the net, apparently it should take no longer than 24hrs to charge a caravan leisure battery ( I am assuming this is what you are talking about) so I would say that it's been cooked being on charge for 4 weeks!!

[yorkshireborn]

at my old place id put the fork lifts on charge at night and when we'd get to work in the morning the batteries would be happily bubbling away before i unplug them.
batteries was never changed in the 7 years i was there.

just assumed boiling batteries was normal.

[DaveG]

Thanks for your responses.
My problem is a simple lack of knowledge and I was hoping that the forum would be able to help but the inclusion of the word caravan appears to have put folk off.
Let's therefore consider a car battery.
1) Does a good battery charger automatically reduce its output to meet the needs of the battery being charged?
2) If the charger & battery are both working correctly is it safe to leave a battery on charge for a lengthy period?
3) How does the charger detect that a battery is fully charged?
4) Could a faulty battery give the wrong "feedback" to the charger?
5) How do I check that a charger is working correctly.

Thank you

[Tadpole]

I think your first line, as I understand things is correct ie once the battery is charged the charger reduces output. Ages since I charged a battery but would have thought a trickle charge for 24 hrs would be my max if it didn’t hold a charge after that for very long, time for a change. imo Lets hope one of the 'tech types' can help some more. Good Luck .................

[davree]

2) If the charger & battery are both working correctly is it safe to leave a battery on charge for a lengthy period?

Thank you

No!!

You should only leave the battery on charge for the amount of time stipulated in the manual. Also unless you have a modern "smart" charger the charge rate will be reduced but not stopped when the battery is full, this is usually due to the fact that if the charger switches off but is still connected to the battery it will drain the battery itself and as such will keep charging the battery(to keep it topped up) until it is disconnected or switched off at the mains

As charging generates heat in both the battery and charger it is "unsafe" to leave a battery charging for any prolonged period of time. A lead acid battery contains a liquid which will be caused to boil by the heat generated by this prolonged period, if the battery in question is a sealed lead acid battery it is even more important to not overcharge it as there is no way for the pressure built up by overcharging to escape.

In your original post you stated that you have had the battery on charge for 4 weeks!! This IMO is way too long for any battery to be left on charge for and TBH would expect a battery charged for this long to begin to boil!!. I have a trickle charger for my car battery which will give a FULL charge after 24hrs.

It could now be that due to the prolonged charging period you have given the battery, both battery and charger have been damaged.

HTH

[boba]

1) Does a good battery charger automatically reduce its output to meet the needs of the battery being charged?

Not quite but nearly.
The cheapest chargers are set to a voltage a little above that of a fully charged battery. As the battery charges its voltage rises and the current from the charger drops. If you leave this sort of charger on for a long time it will 'boil' the battery dry. (It doesn't usually boil of course - just evaporates all of the electrolyte until the battery is knackered).

Caravan chargers are set at a voltage a little below that of a fully charged battery. For current to go into the battery the charger needs to be at a higher voltage than the battery is so when the battery is nearly charged charging just stops. Caravan chargers never charge a good battery fully.

Better chargers read the battery voltage and drop to a very low 'maintenance' charge once it is fully charged. (But see above - caravan chargers don't do this).

2) If the charger & battery are both working correctly is it safe to leave a battery on charge for a lengthy period?

For a cheap charger definitely not - it will destroy the battery.
For a caravan charger usually yes (I've left mine on for several weeks without a problem). But only if the battery is in good condition and the electrolyte level isn't allowed to fall.
For a good quality '3-stage' charger definitely yes. For instance I keep the batteries for my glider permanently on trickle charge (months at a time) with no problem whatever. (Emergency lighting batteries in factories used to be left on maintenance charge for years at a time).

3) How does the charger detect that a battery is fully charged?

It measures the voltage across the battery and for the better ones it also measures the temperature because the voltage of a battery changes as the temperature varies.

4) Could a faulty battery give the wrong "feedback" to the charger?

Yes. If the battery is duff it will go up to a high voltage with quite a small charging current and the charger will think it is fully charged. If the battery has 1 or more dead (shorted) cells it will never reach the correct voltage and the charger will boil it dry trying to get the voltage up.

5) How do I check that a charger is working correctly.

Unless you have the correct equipment and know-how you can't do this properly. There are several sorts of chargers and they are tested in different ways.

For a caravan charger a simple test is to check the voltage with the charger on, no battery and a single small light on - the voltage at the battery terminals should be around 13.8 volts. Be aware that this isn't a very good test though - it just checks that things are roughly working.

HTH