100-Ah or 115-Ah deep-cycle battery in this case?

popotla · Jul 11, 2014

With my 100-Ah starter battery, I want to run in parallel a 115-Ah deep-cycle (using manual split-charge cut-off). Is this Ah difference significant? Would it be better for the deep-cycle to also be 100 Ah, or doesn't it matter?

FlyingPete · Jul 12, 2014

What's the second battery used for- how is the split charge going to be wired and what circuits run from each battery. I can't see much benefit in simply wiring them in parallel. Unless you're going to be running lots of things with the engine off it just doesn't seem worth it.

top-cat · Jul 12, 2014

FlyingPete said:
What's the second battery used for- how is the split charge going to be wired and what circuits run from each battery. I can't see much benefit in simply wiring them in parallel. Unless you're going to be running lots of things with the engine off it just doesn't seem worth it.

I run mine like this, i can have one battery or the other or both,
it means both batteries get equal use and charge and one can jump the other when required. Also very handy for long periods of winching

popotla · Jul 13, 2014

FlyingPete said:
What's the second battery used for- how is the split charge going to be wired and what circuits run from each battery. I can't see much benefit in simply wiring them in parallel. Unless you're going to be running lots of things with the engine off it just doesn't seem worth it.

Between starter battery and deep-cycle, a manually operated "connect/disconnect" switch. I need perhaps 55 amps per 24 hours while the engine is not running.

FlyingPete · Jul 13, 2014

I would at least have a relay that disconnects the second battery when the engine is cranking to prevent drawing too much current from it. If I was building this sort of setup, I'd go for the simple option and use a voltage sensitive relay designed for towbar use. This way the two batteries are automatically separated unless the engine is running and the alternator is charging. Something like this: TF1170-4 - Voltage-sensing caravan combination relay "Mighty Atom" 22 amps rated

This would give you a switched connection to charge the second battery as well as the permanent and switched live connections for the 12S towbar socket- the 'pin 2' connection is no longer required for a post-1998 caravan and can be used instead for the on-board battery.

timtheenchanteruk · Jul 13, 2014

connecting 2 non identical batteries in parralel makes both batteries act like the lower capacity of the 2.

Kwakerman · Jul 13, 2014

timtheenchanteruk said:
connecting 2 non identical batteries in parralel makes both batteries act like the lower capacity of the 2.

Not strictly true as you still have the stored energy of the two batteries available. That said it isn't a good practice as you say, starter batteries are designed for high current short duration use and leisure lower current for longer. If you try to drag high currents out of a leisure battery (like starting an engine) you will end up buckling the plates in the battery and shorten its life dramatically.

popotla · Jul 14, 2014

FlyingPete said:
I would at least have a relay that disconnects the second battery when the engine is cranking to prevent drawing too much current from it. If I was building this sort of setup, I'd go for the simple option and use a voltage sensitive relay designed for towbar use. This way the two batteries are automatically separated unless the engine is running and the alternator is charging. Something like this: TF1170-4 - Voltage-sensing caravan combination relay "Mighty Atom" 22 amps rated

I could (not saying it's the most convenient way of doing it but it's the way that's already in existence---the set-up I already have) just ensure that when starting, the second battery is separated and thus protected from too much current draw, and join the two when the first has had time to charge up.

SteNova · Jul 14, 2014

Kwakerman said:
If you try to drag high currents out of a leisure battery (like starting an engine) you will end up buckling the plates in the battery and shorten its life dramatically.

what about these?

Kwakerman · Jul 14, 2014

SteNova said:
what about these?

Nothing against them and heard good things about them but they are a hybrid of the two types. As with most things something designed specifically for one task will do that task better than a jack-of-all-trades one designed for multiple uses.

100-Ah or 115-Ah deep-cycle battery in this case?

popotla

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FlyingPete

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top-cat

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popotla

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FlyingPete

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timtheenchanteruk

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Kwakerman

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popotla

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SteNova

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Kwakerman

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