Charging 2 Batteries in ||?

Question

I'm thinking about adding another deep cycle battery to my boat's electrical setup.

For a 2 battery, 12V system (2 12V batteries wired in parallel), which option is best to get a full, even charge on both batteries overnight?

* B1(+)=battery 1 positive, C1(+)=charger bank 1 positive, etc

Option 1: C1(+) to B1(+), C1(-) to B1(-)

Option 2: C1(+) to B1(+), C1(-) to B2(-)

Option 3: C1(+) to B1(+), C1(-) to B1(-); C2(+) to B2(+), C2(-) to B2(-)

Will this option work with the jumpers connected?

If both charger banks are 5A (for example), would it charge the whole system using essentially a 10A current?

Answer 1

Get a battery isolator bank at an auto parts store. All of the negative leads go to a common buss point. The charger will go to the isolator common post, put one battery common to each of the other isolator posts. This will give a balanced charge to the two batteries. You should also add a battery selector switch so you can use one or the other or both batteries when needed. The isolator is about $40, the switch maybe about the same.  Use caution about an auto part in a boat, explosions can occur if the wrong part is used. Marine rated parts are safer.

Answer 2

plus to plus would work but so would another charger... you might think about getting another be smarter but anyway just jump it the same way to the other will work

Answer 3

Option 1 and 2 will both work if you leave the batteries connected in parallel.  For option 3 you are better off disconnecting the batteries from the parallel circuit before connecting to 2 separate chargers.

Answer 4

Since the batteries are wired in parallel, it doesn't matter which battery you hook the charger to, they have the same voltage potential. They will be balanced because of the wiring, so they will be charged equally as well. The only difference would be it will take twice as long to charge two batteris with the same charger that you would use on only one battery.

Just hook the charger to which ever batter is easier to get to (Option 1 or 2).

If you use two chargers, you would add the current ratings together, giving you a 10A charger.