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Old 05-15-2009, 02:01 PM   #1
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1974 25' Tradewind
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Dual Batteries

Question. Can I charge 2 batteries simultaneously hooked together in parallel with either a portable charger or on-board charger. Since I'm new to this and don't want to damage my newly renovated ship, I'm seeking knowledge of how to set this up.



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Old 05-15-2009, 02:27 PM   #2
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If you leave them hooked together for a long time, the weaker one will tend to drag down the stonger one. Not a problem while charging though.

If they're identical batteries made at the same time, they should work well together.

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Old 05-15-2009, 02:30 PM   #3
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Don't forget they should be the same size, type, age, and amperage.
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Old 05-17-2009, 09:15 PM   #4
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re "the weaker one will tend to drag down the stonger one" - common myth but not quite that simple.

It is good advice to try to match batteries in a bank as closely as possible to aid in longer life but a 'weaker' battery will not damage or destroy a stronger one or drag it down as long as they are the same chemistry. What happens is that the stronger one just works harder in proportion to its strength compared to the weak one. All batteries of the same chemistry in a parallel bank will give and take charge in proportion to their capacity.
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Old 05-17-2009, 09:47 PM   #5
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You can charge em' both at the same time...

If you're using a 'portable' charger, when the batteries are hooked in parallel (pos - pos, neg -neg) it's best to hook the POS charge lead on one battery, and the NEG charge lead on the OTHER battery - that way you'll have about the same level of charge for both, as the resistance in the parallel cables and connections tend to even out.

If I'm setting up a battery bank, I like to hook up the cables going to the Load, in the same manner...however your batteries probably aren't hooked up that way in your trailer, at lease mine aren't - each pair of leads come into the fuse panel and are hooked together there - but it works just fine.
Ray & Pat; Morada, CA
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