Dual habitation batteries - advice please.

[KiwiKampers]

I have a factory installed pair of parallel 12volt habitation batteries as supplied by Autotrail four years ago. At the same time Autotrail fitted a solar panel. Having noticed that the batteries do not appear to hold their charge I have taken them to an auto electrician to have them checked. He tells me one is OK and the other is dead. He is recommending I change the pair of them, rather than just the faulty one. Alternatively, he has suggested a pair of 6 volt batteries wired in series.
I should point out that we are regular wild campers and rarely use a EHU.
My questions are:
1. Why should I replace the good 12 volt battery as well as the faulty one?
2. Autotrail fitted a pair of 12 volt parallel batteries, but are a pair of 6 volt batteries in series a better option?

 

[Jimbohorlicks]

Why not replace the 2 and keep the better one as a backup or wire it in with the others. If it pulls them down just keep it separate.

 

[Jev88]

As above - the weak battery will pull and put "strain" on the good battery. I too am looking at the 6V T105 Trojan battery route as when put in series to get 12V they contain collectively more power and are designed to tolerate deeper discharge if the blurb is correct.

 

[bigtwin]

Why not replace the 2 and keep the better one as a backup or wire it in with the others. If it pulls them down just keep it separate.

How would you detect if the older battery was pulling the others down?

Ian

 

[IanRJ]

As above - the weak battery will pull and put "strain" on the good battery. I too am looking at the 6V T105 Trojan battery route as when put in series to get 12V they contain collectively more power and are designed to tolerate deeper discharge if the blurb is correct.

My own recent investigations have found that the 6v Trojans are both much taller and heavier than the typical 12v. For that reason, I have dropped the 6v idea!

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[Lenny HB]

How would you detect if the older battery was pulling the others down?

Ian

By running a controlled discharge test on each battery then another test with them connect together.

If they are flooded wet cells best to replace both, if they are Gels you could get away with just fitting one new one.

 

[Jev88]

How would you detect if the older battery was pulling the others down?

Ian

Different internal resistance I think. Expensive experiement though - destroying the good battery?

 

[Stealaway]

Trojan T105 are good. Just remember that two in series at 12V they will be a total of 185Ah -- is that enough?

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[Jev88]

My own recent investigations have found that the 6v Trojans are both much taller and heavier than the typical 12v. For that reason, I have dropped the 6v idea!

Yes, they tend to be taller but not an issue for me. 6V Trojan has 185ah. Very expensive to get that power in 12V unit.

 

[bigtwin]

Why not replace the 2 and keep the better one as a backup or wire it in with the others. If it pulls them down just keep it separate.

I read the above post as implying that you could deduce this situation with the batteries installed.

By running a controlled discharge test on each battery then another test with them connect together.

I agree that your method might (?*) give an indication but could only be implemented off board (well, disconnected as a minimum).

* wouldnt this method just tell you that you have a ‘faulty’ battery (i.e. one that won’t hold a charge)? In which case you wouldn’t install the faulty battery.

Different internal resistance I think. Expensive experiement though - destroying the good battery?

There is no suggestion that the old battery is faulty; in fact the OP has had it ‘tested‘ and verified ok. I think that my question to Jimbohorlicks remains.

Ian

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[Jimbohorlicks]

Bigtwin, I was responding to the original poster, really not interested in arguing with you.

 

[bigtwin]

Bigtwin, I was responding to the original poster, really not interested in arguing with you.

Sorry if you saw it that way, I was only asking a question that I, and I suspect the OP, would find the answer to very useful.

Ian

 

[Jev88]

Sorry if you saw it that way, I was only asking a question that I, and I suspect the OP, would find the answer to very useful.

Ian

I am happy to learn too. Was always told not to mix different ages of battery. Internal sulphication changes the internal resistance so the weaker/older battery will "pull" more power to try and achieve full charge which potentially exposes the newer battery to overcharge, shortening its life.

 

[autorouter]

Trojan T105 are good. Just remember that two in series at 12V they will be a total of 185Ah -- is that enough?

185Ah is the '5 hour' rate - for comparison with other batteries use the '20 hour' rate, which is 225Ah.

 

[autorouter]

6V Trojan has 185ah. Very expensive to get that power in 12V unit.

Remember that's 6 volts. It has the same total energy storage as a 92.5Ah 12V battery. Total energy = amp-hours x volts = watt-hours.

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[KiwiKampers]

Thanks very much. I’ve learned a lot. It also confirms that the auto-electrician is honest and not trying to sell me two batteries where one would have done.

 

[Captain Yoghurtpot]

Can anyone advise me please on a new single 12 v leisure battery.
Current one is a lead acid type and made by pro-max.
Can’t find out what amphour it is but it says part no.100 on it and I don’t know how old it is (was in the van when we bought it in 2018).
Seems to work fine and charges correctly ( I think ) when put on charger from the van.
Am thinking of doing some short run wild camping (2 to 3 days max) or non EHU site camping in UK only and am only presently to run lights, which all have LED replacements, and the water pump. Fridge and Heating/Hot water can be on gas.
Have not bought one but am considering an inverter to just run a laptop and slow cooker, and also a portable solar panel to help with charging of the leisure battery.
Don’t have room for a second leisure battery as a permanent fixture but may consider taking the old battery as a spare to the new one.
What would anyone recommend.?
Van is as avatar and 19/20 years old.
Thanks
Iain

 

[Nasher]

Rather than use an inverter for your laptop look for a specific lead for your laptop that will take 12v it will be more efficient than an inverter

A slow cooker on an inverter will kill the battery very quickly

I have a single 110Ah battery and manage 3 days on that with a compressor fridge, so you should be OK without the slow cooker and depending on how much you want to use the laptop.....?