Geez, you're getting all kinds of info here - let me confuse you more.
Are both batteries the same? If so, alternate between the 2 like they said above.
If one is a starting and the other a deep cycle - then it's clear.
BUT, I can tell you this: on MY Perko switch, only the battery it's switched to will charge when running. So, if you do have 2 different batts, you need to be sure that you recharge that starting batt before you switch it to the deep cycle - if you have the standard old style setup like I do.
There, clear as mud
