Starting Battery Discharges While Running

I just boat a used boat with mercruider i/o. It is equiped with an alternator and that is hooked up to the starting battery, theoretically. I haven't verified. I took it out for the first time today and it ran great. When I picked it up the previous owner stated he hadn't taken it out in a few weeks or charged it. Since it started fine in my driveway I figured it had enough juice. When I started it at the ramp it was a little sluggish but fired up and then we ran it for about 30 to 45 minutes out on the lake. Fortunatly, I didn't shut it off until I was near the ramp. When I tried to fire it back up the battery was dead. I used the trolling motor hooked up to the other batteries to get to the ramp and to lift the outdrive. <br /><br />I was showing about 12 volts before starting and about 13 or 14 while running. Now it it shows about 9. Shouldn't the starting motor have charged while running? If I could start it at the ramp and it charged while running it should have been fine. What would make it discharge? Bad battery? Bad alternator, regulator or maybe wiring? Amy ideas to get me started would help.

Re: Starting Battery Discharges While Running

You need to charge the battery and get it load tested at a battery place to be sure its good<br /><br />3 to 5 years is a good life <br /><br />When you have a good battery you need a DMV to test it<br /><br />It should hold around 12.6 to 12.8 volts and when the motors running it should be in 13.8 to 14.4 range more or less<br /><br />tommays

Re: Starting Battery Discharges While Running

Now I am a little perplexed. The boat has sat in my driveway for about 2 hours. I haven't charged it or changed anything. Now it reads about 12.5 volts and fired right up. It was dead, 9 volts or less at the lake. What gives?

Re: Starting Battery Discharges While Running

You've got a bad, bad battery. Check it with a hydrometer - bet you find at least one dead cell.<br /><br />had a car battery like that once - don't understand how, but it happens

Re: Starting Battery Discharges While Running

A bad battery post, cable, internal cell problem can cause intermittent battery problems. The solution is a new one.

Re: Starting Battery Discharges While Running

I did clean all the posts and terminals. I will see how it works. If it continues to act up, a new one is in my future.

Re: Starting Battery Discharges While Running

Hi Dan,<br /><br />Batteries don't repair themselves. Do yourself a favor and get a new one. It's a real headache when you're on the water and you have no power....

Re: Starting Battery Discharges While Running

As an update, I took the boat out again today. Made sure the starting battery had a full charge before we left. We ran around for about 1/2 an hour then shut her off near the ramp. She fired right up. I shut her down a few more times and she fired up right away each time.<br /><br />That being said, I agree that a battery won't repair itself. I do know the previous owner charged it only ocassionally when not being used and it sat for periods not being maintained. The battery may have gone dead or been overcharged. Therefore, to be safe I am going to replace the battery and get an onboard charger. Thanks for all the help.

Re: Starting Battery Discharges While Running

You've got bigger gonads than I do. If I had a battery that could have left me on the lake but by sheer good fortune didn't, and I couldn't diagnose exactly why and fix it, that battery would be history.<br /><br />When I'm out on the water I don't play around. I've had storms come up on me so fast that had the engine not started I may not have lived to talk about it.

Re: Starting Battery Discharges While Running

I actually suspect that the problem has nothing to do with the battery, but rather the connections. As broken batteries don't repair themselves, dead batteries shouldn't recharge themselves. When the battery "died" I got nothing out of it and nothing would work. It wasn't acting worn down, it was acting DEAD. Two hours later without any further charging, it started the motor like it was nothing and has worked perfectly since. The battery might not be in perfect condition, but I don't think it is broken.<br /><br />The connections, however, were corroded and poorly made. A little cleaning and they seem to be working, but they will get redone correctly when I get the new battery. I could be wrong and it is the battery, but I don't think so.

Re: Starting Battery Discharges While Running

Broken batteries do indeed fix themselves - intermittently. Battery posts frequently break just beneath the top of the case. The weight of the battery cable bouncing around can cause the connection to be made and then open again at the next jarring. Connectors between cells also break although it is rare.

Re: Starting Battery Discharges While Running

Glad you got it fixed, Dan. Those connections can cause havoc and headache. Probably was a bad connection after all....But better safe than sorry...