Help troubleshoot battery, shoud I even Stay with dual battery?

[JoDo]

Hi Guys, when I got my 1989 2000sc it had two batteries in it. This was 3 years ago and it always was slow cranking. Like a bad connection where you turn the key and nothing, then maybe a short turnover and then a faster turnover and start. No rhyme or reason, each time was different. I replaced one battery two years ago and the other just last week with a Super Start 800 cold cranking amps battery. I also replaced the starter solenoid that is screwed to the plywood partition between engine and battery. It still did not start normal. Today while on the lake I went to restart the engine (which had started fine a few times before) and nothing. I kept turning the key because normally it would finally turn over enough times to start but it didn't. What happened was smoke started billowing from the battery compartment. The wire I had connecting both negative terminals of each battery together got so hot it melted and even the lead terminal on one of the batteries is a bit deformed. I eventually just hooked all wired to the one new larger battery and it started perfectly. Better than it ever has since I've owned it. I'm wondering if the two batteries were wired together correctly from the start. What could have been the issue? Should I just stay with the one battery since everything seems to work so much better? Is there a diagram to show me exactly how the two batteries should be hooked up on my year and model of boat? I'm a bit confused. Thanks everyone.

[mmwjr]

It sounds like the negative battery cable connecting the two batteries was bad and had high resistance from either corrosion or bad crimps on the lugs. Were you always trying to start with the battery switch in the "BOTH" position? This will double the CCAs and should result in a easier start but if he cable was bad would give you the results you mentioned.

I have two batteries and use one on one outting and switch to the second battery the next time out, this keeps both charged and one is always isolated as a back up.

[JoDo]

Thank you Mike, I do not have a battery selection switch. It was a fairly light gauge stranded wire with crimp on ends. Maybe one wing nut was a bit loose?

[mmwjr]

What gaugae was he wire? If undersized then that equals high resistance when drawing high current. I would use a heavy gauge wire (2awg) and install either a switch or an isolator. West marine has wiring diagrams on different setups or just google marine dual battery wiring diagrams.

[JoDo]

Oh man, it was thin wire. Like 12g maybe. I will definitely replace it with the proper gauge and install a switch. Thank you.

[mmwjr]

Wow, 12 gauge when drawing 100's of amps. Sounds like smoke to me

Glad to help, enjoy the rest of the season

[shrew]

You're batteries are not wired together properly. 12G is far too small. Get a marine mechanic in there to fix whatever the previous owner did. poor connection and small wires will cause what you're dealing with. Also, if you are running batteries in parallel should be done with the same size, type, capacity batteries. You treat should treat a parrallel battery bank like a single battery.

Make sure the connections on the starter aren't corroded.
Make sure the ring terminal on the starter isn't corroded.
make sure the connection on the ring terminal on the starter is solid.
Make sure all cables are properly sized
make sure all ring terminals are properly crimped
make sure all ring termials are tightly fastened.

If you have two batteries install an isolation switch. Start the boat on one battery and use the second as either a 'house' battery when the engine isn't running, or a emergency secondary battery. You'll need to put both batteries on a chargine system to keep them topped off.

[JoDo]

Thanks to you as well Shrew. I agree something is not wired right and will get it properly wired with an isolation switch.

Make sure the connections on the starter aren't corroded. THIS I HAVE DONE, LOOKS GOOD
Make sure the ring terminal on the starter isn't corroded. LOOKS GOOD AS WELL
make sure the connection on the ring terminal on the starter is solid. DITTO
Make sure all cables are properly sized THIS NEEDS ADDRESSING
make sure all ring terminals are properly crimped WILL CHECK ALL THESE
make sure all ring termials are tightly fastened. WILL CHECK ALL THESE AS WELL

[JoDo]

Update: I have now learned that that was not a starter solenoid but a battery isolation switch. I replaced three "wires" with proper sized cables. One being the ground connecting both battery negatives together and the other two are positives to each battery from each side of the isolator. Works normal, cranks normal, seems to be charging. Thank you everyone.

[mmwjr]

Glad to hear your issue has been resolved, enjoy therest ofhe season