this is the 2 bank one i run.works great and have no problems with it.they make it in a 3 bank version as well.
On a side note. do you have a battery switch?I know i wired mine up so when im sitting just running the radio i change the switch over and it takes the cranking battery out of the loop. as i to have drained both batteries just jammin out at the beach and do not want it happen again.so far the combo of a charger and changing the switch over have kept me cranking all day and every time.