Mixing 6-volt and 12-volt Batteries? - SailNet Community

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Old 11-08-2008
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Mixing 6-volt and 12-volt Batteries?

I need to replace my two 12-volt batteries. They are setup as two independent banks with a standard 1-2-both master switch. I would like to replace these with the more durable and higher amp/hr rated six volt batteries. My problem is I don't have enough space for four 6-volts. I can fit two 6-volts (225 amps) into the space now occupied by the two 12-volts (bank one). I then have only enough room for one 12-volt (130 amps) in another locker (bank two). Any ideas about mixing battery banks with different amp ratings?
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If the two 12 volt batteries you are replacing are 130 A each then replacing them with two 6 volt 225 A batteries will give you less capacity than you had before. The 6 volters would need to be connected in series for 12 volts @ 225 A, while the 12 volters were connected in parallel for 12 volts @ 260 A

Plus those ratings seem like peak current ratings which don't mean that much. You need to see what the battery capacities are in Amp-hours. Perhaps the ratings you listed there are indeed amp hours.

To answer your question, using batteries of differing capacities in parallel is ok but not ideal. Charging them could be a problem depending on weather they are charged seperately of as one big pack, and also how quickly they are charged.

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Old 11-08-2008
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The other problem with having a 12 VDC battery bank of just two SIX Volt batteries is that if either goes dead, you lose the entire bank... That is why I highly recommend any battery bank made up of SIX volt batteries be four-batteries minimum.
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Old 11-08-2008
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T105 6V batteries ARE generally rated around 225@hours at the 20 hour rate, thus two of them will rate 225@hours @ 12V. This will be a reduction in your amphours, but if the construction is better than the 12V your were using, it may be worth the tradeoff.
I am not aware of any standard 12V battery size that rates 130amps at 20 hrs.. The group 31's typically rate 100-110 and the 4D's are generally over 150-160. What exactly do you have there?

In any event...there is NO problem mixing 12V batteries with 6V batteries paired as 12V's as long as the construction type is the SAME...i.e. flooded or AGM or GEL.

I think Dawgs concern is misplaced...as even if you lose the 2 6V batteries...you will still have a working 12V battery. If the pair of 6V's were your only source then I would agree.
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