Adding batteries in parallel

[J4mie82]

Hi,

I would like a quick bit of advice as I'm not 100% sure what I'm doing. I want to add to batteries in parallel but the batteries are if different ah capacities. One is a 12v 88ah battery and the other is 110 ah.

The 88ah is an alphaline leisure battery and is 6 months old and has been constantly topped up by a solar panel.

The 110 ah is a lucas leisure battery and is brand new.

Is there anything I should be worried about or should check after connecting them in parallel?
When charging will the 110ah get to full charge connected to the 88ah battery?
Will there be any sparks when connecting them?

Any advice would be helpful as I understand the idea but not confident it will be safe.

[J4mie82]

I want to add two batteries*

Auto correct gets annoying!

[Wy_White_Wolf]

Expect a very short life out of the batteries.

They will have different internal resistances that will cause one set to be constantly overcharged and the other to never fully charge. They will also discharge at different rates.

WWW

[J4mie82]

So in short, don't do it.

Cheers for that glad I asked first

[SunEagle]

So in short, don't do it.

Cheers for that glad I asked first

You just learned a valuable lesson that a solar battery system can not "grow". The batteries should always be the same voltage & Ah rating size. They should also be relatively the same age when you start to use them. Adding a new battery even to a 6 month old system can still cause charging and discharging issues.

[Mike90250]

Don't, all the batteries will fail early. But, you could , just expect to have shorter lifetimes. Just start saving for the right size battery bank for the future.

[J4mie82]

Would there be anyway if charging them simultaneously with a solar panel?

[SunEagle]

Would there be anyway if charging them simultaneously with a solar panel?

You can charge each battery by itself but then you will have to use each separately.

If you hook them up together they will not charge or discharge evenly and both will die an early death.

[J4mie82]

You can charge each battery by itself but then you will have to use each separately.

If you hook them up together they will not charge or discharge evenly and both will die an early death.

So that's a no.

I think I realise I can charge them seperately haha thanks for the advice tho. It's a bit gutting I would if bought 2 at once.

When could you add 2 batteries with different amp hour capacity?

[SunEagle]

So that's a no.

I think I realise I can charge them seperately haha thanks for the advice tho. It's a bit gutting I would if bought 2 at once.

When could you add 2 batteries with different amp hour capacity?

You really should never have batteries with different amp hour ratings connected together. The batteries resistance will cause them to charge and discharge unequally which will shorten their life.

[J4mie82]

I have just checked the Brand new un used lucas battery and it is only 12.4v I would expect it to be 12.7?

Would you recommend I return it and get 2 batteries together that are the same?

[SunEagle]

I have just checked the Brand new un used lucas battery and it is only 12.4v I would expect it to be 12.7?

Would you recommend I return it and get 2 batteries together that are the same?

I do not have first hand experience with the Lucas leisure battery. Some new AGM type batteriers may be sitting at 12.4v when it is sold with expectations that it gets charged up before going into service. So it could be bad or maybe not. If it can be returned for a full refund then you can try that.

Whatever decision you make, all of your batteries have to have the same voltage and Ah rating.

[Mike90250]

....When could you add 2 batteries with different amp hour capacity?

Only when you have to keep Grandma's Iron Lung running in an emergency. Otherwise, you are damaging both batteries.

[SunEagle]

Only when you have to keep Grandma's Iron Lung running in an emergency. Otherwise, you are damaging both batteries.

You better have a big battery for that Iron Lung.

Heck I can't even run an Oxygen machine ~ 300 watts for 8 hours with my 12v 200 Ah battery system.