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Old 08-05-2009, 13:16   #1
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Battery Boost

Just bought a spare 12 volt battery to use if the other 2 run down. When boosting with cables do you attach to just one of the batteries or the positive on one and the negative on the other. I have a common 2 battery set up in series with the usual switch (off, on, 1, 2 or both batteries).

thanks...
Gary
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Old 08-05-2009, 13:53   #2
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Connect your boost battery to the positive on one, and the negative on the other house battery, just as you would for a permanent parallel connection.
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Old 08-05-2009, 23:09   #3
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hold on guys, I think the OP writes "series" where he means parallel??!! That switch only works when you have two 12V batteries for a 12V installation, not with two 6V batteries for a 12V installation.

My advise is to make the house bank bigger and leave the switch to "1". When the house bank gets too low, start to engine/genset to recharge; they use bank "2" for starting. Never use "both" unless during emergencies.

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Old 27-05-2009, 14:01   #4
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Battery

...NIck.. thanks for post...

I have 2 12volt batteries .... does Gord's advice prevail? ... i.e, if both batteries run down I would connect booster cables from my spare "booster battery" to the positive on one of the 12 volt batteries and connect the negative to the other 12 volt battery. Having done this I would then set my battery switch to "both" and try to start the engine.

Also: If I want to charge up my spare 12 volt "boost battery" (I have solar panels) would I just do the same thing (as if I was going to boost the batteries to start the engine) and then would my solar charging setup then charge all 3 batteries?

thanks in advance
Gary
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Old 27-05-2009, 19:28   #5
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bcguy,

no, what I would advice if your batteries can't start the engine:

- put battery switch to "off"
- use jumper cables or better yet normal cables with lugs between the spare battery and the starter on the engine
- start engine
- put switch to both
- remove spare battery

If you connect the spare battery to the other two (which are empty) you discharge the spare battery into the empty ones. Better use it to start the engine.

After starting engine, reconnect the normal batteries before removing the spare battery. If you remove the spare first, you can blow out diodes in the alternator (it must always see a battery).

cheers,
Nick.
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