frustrating.  i took the boat out,  and after awhile of swimming it didn't start. switch to my second battery completely dead.  called over mike at sea tow for a jump,  got hooked up and the boat would not even engage the starter.  the only thing i can really think of is i put in a new battery switch and i had this happen on the dock, i took the switch apart and re did all connections. so i didn't like that switch it was not a perko it was some brand academy sells.   so i bought a perko yesterday and i will install tomorrow.  any other ideas?

Start with a really good charge off a trickle charge as he said. If you use your boat enough with one battery drawing down for the stereo, then switch it to both...it will leech charge from the cranking battery and before you know it you have two weak batteries.

Trickle charge them both and see what happens.

Start there.

dang guys thanks for the good advice.  here is what happened.

got to the boat to meter both batteries at 12.54 volts.  hmm see no problem with power source.

switch perk(actually off brand from academy)  and notice that i get nothing from batter one when switched and only 8 volts from battery 2.

next i replace the the off brand switch with the trusty perko thats been around for years.  and walla i have 12.54 volts on either switch side.

okay time to test, give the key a turn and nothing.  bummer

meter at the starter and i have power,  meter the the lead coming in to engage the starter and have power when i turn the key. 

so then i pulled the starter and erikson actually sold me one for 185 (going rate on internet checked my favorite parts place before i left)  through it in ten minutes later had a nice boat cruise.