Gee, this discussion became convoluted. Your maximum draw on the circuit
would be when starting. Your battery may be rated in peak starting amps
capacity. One of the advantages of 24 volts over 12 is the ability to
use smaller diameter wires (weight savings). So, using the same diameter
for interconnection as was used for the 12 primary connection is
overkill. Low of mentioning of twice the voltage then half the wire
diameter...but I thought it was 1/4, but I am not an EE and it has a
loooong time since I have played with those calculations.{no, I don't
want to do the calculations right now! ;-) }

wrote:

I am putting two 12V batteries together
http://www.batterymart.com/p-hawker-...t-battery.html
to make a 24V battery.

What size cable should I use to make the serial connection?
http://shop.genuinedealz.com/Marine%...ttery%20Cable/

Thanks,
Karl