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you can hook up two batteries in parallel which just increases the ah/charge they hold. lots of yank cars do that. very simple system. however, you want to make sure they are the same battery and age, else you can get one pulling the other down.
it also wouldn't separate the battery, so you couldn't drain just one down like going camping.
if you want to drain one for camping then the easiest way is to use a voltage sensing split charge like CAMPER VAN SELF SWITCHING, SMARTCOM VOLTAGE SENSING SPLIT CHARGE RELAY-12V / 30A | eBay
this only turns on when the alt is kicking out juice. one thing to watch out for is if the battery is drained right down it may wish to draw more than 30amps and will burn out the relay, but you an just use the split charge to trigger another higher relay like 12V Heavy Duty Split Charge/Winch 200A Relay - Car Van Boat - 200 Amp - 4 Pin | eBay but you may want a better make, like durite.
so, if you aren't going to drain your second battery all the way down then the 30amp voltage sensing relay is probably fine, fit a 20/25 fuse to protect it. if you always blow fuses because you drain too much juice, then add a 200amp relay triggered by the voltage sensing relay.
oh, and use a leisure battery. it's designed for deep discharge.
hope that makes sense
it also wouldn't separate the battery, so you couldn't drain just one down like going camping.
if you want to drain one for camping then the easiest way is to use a voltage sensing split charge like CAMPER VAN SELF SWITCHING, SMARTCOM VOLTAGE SENSING SPLIT CHARGE RELAY-12V / 30A | eBay
this only turns on when the alt is kicking out juice. one thing to watch out for is if the battery is drained right down it may wish to draw more than 30amps and will burn out the relay, but you an just use the split charge to trigger another higher relay like 12V Heavy Duty Split Charge/Winch 200A Relay - Car Van Boat - 200 Amp - 4 Pin | eBay but you may want a better make, like durite.
so, if you aren't going to drain your second battery all the way down then the 30amp voltage sensing relay is probably fine, fit a 20/25 fuse to protect it. if you always blow fuses because you drain too much juice, then add a 200amp relay triggered by the voltage sensing relay.
oh, and use a leisure battery. it's designed for deep discharge.
hope that makes sense
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