Batteries won't stay charged.

[Mani]

For the second time this season my batteries have drained themselves out on the lake. The first time around I wrote it off as two things. First I didn't charge them over the winter. Second I was trying to charge both batteries off my alternator at the same time, and I figured it didn't have enough juice to do that and killed both.

Yesterday, it happened again and I had to pay the lake tow guys to come get me. This time my reserve battery that I had never turned on through the selector switch was dead, so I figure that one is just bad, but the other one only had enough juice to barley crank the motor (the engine died on the lake while we're wakeboarding). Not fast enough to start.

I've had the battery tested, and it checks out fine. My mechanic said he had the alternator tested and it checked out fine. Faulty wiring maybe? What's a good replacement alternator that can put out a good amount of juice?

TIA,
Mani

[wotan2525]

Just to clear something up -- both of these batteries were charged 100% before you put in the water?

Something is draining them and draining them fast... and if you know the batteries are good (how old are they?) and you know the alternator is good then you don't have too many options. Is this an old alternator with an external regulator? When I bought my boat they had it wired wrong and the same thing was happening. I switched to a 1-wire alternator from DB Electrical and have never had another problem. I think they sell a 105 amp marine alternator for ~$120.

If it's not an alternator wiring problem, though, this isn't going to solve anything. Is it possible that your battery charger is faulty? I'm thinking it may have charged your battery enough to get the boat started but the stock alternator is pretty weak and isn't going to do much more than keep it charged while running -- unless you're running for hours, I wouldn't expect your alternator to recharge a nearly-dead battery.

[Mani]

Both got charged about a three weeks ago. The #1 held it's charge for about a day and then died. It won't even turn on the guages, and it's an older battery that came with the boat. The #2 battery is a duralast Marine dual purpose with 1000 CCA and it held it's charge until the about the 5th time I started the motor yesterday. The engine would bog down if I gassed it from a stand still but would get going with a split second after the bog down. The last time it just died.

The marine mechanic who put my motor back together said that he was having some trouble with the alternator and that's why he had Autozone bench test it. He says he thinks the connections were just loose, since Autozone's test said it was good. The alternator and it's wires, and the distributor are the only things on the ignition and electrical side that didn't get replaced in my rebuild. I did, however, change out the rotor on the ignition.

Any chance the Autozone guys didn't test it properly, or that the alternator is just too week to power the battery? The previous owner had it changed out about three years ago.