Mixing Batteries

[Philiom]

Hi, I have a 100 ah Leisure Battery in my Motor Home, I would like to add another, what would be the downside to using a starter battery instead of another Leisure Battery as I have a spare Starter Battery, would welcome any comments ( good or bad haha!).

 

[Jev88]

Ideally the leisure batteries should be same type, same size and same age..... or risk one working harder than the other and dying prematurely.
I am sure more expert answers will be along shortly.

Do remember that engine starter batteries are built for large output, short time where as "leisure" batteries are low output for long time.

 

[Spriddler]

WRT using a 'starter' battery, I only have one habitation battery, a 90Ah 'Bosch Silver' wet lead/acid STARTER battery (because it was free to me) and it's been in use for 7 years and still going strong without any issues. No solar, no B2B, no inverter. It powers the 12v control circuitry for the gas hot water, gas heating (rarely needed) and gas fridge (on 24 hrs), plus lights, water pump, phone and tablet charging. I often go four stationary days off grid when competing in motorbike events and could probably go a couple more days in summer light evenings before needing a charge if the voltage had dropped to around 11.8v.
I think the suitability of a lead/acid starter battery for 'leisure' use would depend upon the type of work it's expected to do, although as already said, mine has been fine running my low drain applications.
Obviously with the extra battery capacity you'll need to be able to keep both of them charged, either by EHU, solar or driving.

 

[Lenny HB]

If the battery in the van is more than a year old it would be best to buy two new batteries.

The Bosh Silver that Spriddler quotes is the same as the old Varta LDF90 which was sold as a dual purpose battery and works well as a leisure battery, most starter batteries don't.

 

[Spriddler]

The Bosh Silver that @Spriddler quotes is the same as the old Varta LDF90 which was sold as a dual purpose battery

Well there's a thing. I didn't realise that. Slap my thigh!

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[TheBig1]

A lot of so called leisure batteries are starter batteries with a different sticker. Mixing different size/age/type batteries is that in theory you get the combined capacity, but in reality both perform at the characteristics of the weakest battery. So if one is older and starting to fail, they both will

 

[Philiom]

Thanks for all the replies, one other question, how do I measure the wires to the existing leisure battery as I will need addional wires for the extra battery so need them to be the same rating, I am guessing the diameter of the copper wires is what is measured, just need a bit of knowledge on calculating the existing wires.

 

[autorouter]

how do I measure the wires to the existing leisure battery as I will need addional wires for the extra battery so need them to be the same rating, I am guessing the diameter of the copper wires is what is measured, just need a bit of knowledge on calculating the existing wires.

The amps rating of the wires depends on the cross-sectional area (CSA) in square millimetres. For example 8mm². The CSA is often printed or stamped on the outside of the cable. If it's stamped, it shows up better if you shine a torch at a shallow angle. If you can't find the CSA from the writing, then as you say you can measure the outside diameter and look it up in a table such as this one.

Cable size table | 12 Volt Planet

A guide on cable sizes from 12 Volt Planet

www.12voltplanet.co.uk

Scroll down to where it shows the diameter of the cables. But if you just choose cable with the same or larger diameter you won't go far wrong.

 

[Philiom]

The amps rating of the wires depends on the cross-sectional area (CSA) in square millimetres. For example 8mm². The CSA is often printed or stamped on the outside of the cable. If it's stamped, it shows up better if you shine a torch at a shallow angle. If you can't find the CSA from the writing, then as you say you can measure the outside diameter and look it up in a table such as this one.

Cable size table | 12 Volt Planet

A guide on cable sizes from 12 Volt Planet

www.12voltplanet.co.uk

Scroll down to where it shows the diameter of the cables. But if you just choose cable with the same or larger diameter you won't go far wrong.

 

[Philiom]

Thanks for the info

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[dunnah01]

Thanks for all the replies, one other question, how do I measure the wires to the existing leisure battery as I will need addional wires for the extra battery so need them to be the same rating, I am guessing the diameter of the copper wires is what is measured, just need a bit of knowledge on calculating the existing wires.

The wire size will depend on the difference in amps between the batteries. If you mix batteries you risk having a large difference so you'll need big cables to take the current. The current to the hab stuff won't change.