Battery issue & question

[Augoose]

I've got a 1989 4.3 mercruiser w/ Alpha I. The problem I'm having is a battery drain issue which started several weeks ago. After just a few days, the battery was completely dead (0 volts on both multimeter + dash voltmeter gauge). I thought I had found the problem (float switch), but today after letting the boat sit for about 2 weeks, the battery is dead once again (dash voltmeter gauge read at about 9 volts). For the heck of it, I tried to start it anyway but all I got was a click.

I then pulled the battery off the boat and headed home to hook it up to my trickle charger. When I got there and hooked it up, the charger immediately gave the "charged" light indicator. I checked it with a voltmeter (charger disconnected) and sure enough - 12.1 volts on the battery.

I didn't bother driving back to put it back in the boat and test it, but it sure made me confused. The only other thing to add is that this is a 6 week old Interstate Starting battery that, through the course of having to figure out this drain issue, has been drained completely to 0 volts twice, and drained to below 10v once.

Could this battery be damaged in such a way that it could show 12 volts with a meter but not have enough cranking amps to start?

If the battery is good, is there anything in the boat's electrical system that could cause the system to "think" there is only 9v when there is really 12v? Starter solenoid, etc? The battery is new, the cables are new, and as of two weeks ago, the boat was starting and running normally.

Thanks!

 

[fossill]

Re: Battery issue & question

Charge it up and then load test the battery. Any auto parts store will usuallly do for free and tell you condition of battery.
If it checks out ok, check your alternator. If it's toast, replace it and check the alternator too. It's the usuall culprit in an electrical drain due to a bad diode or rectifer.

 

[Silvertip]

Re: Battery issue & question

12.1 volts is NOT charged. 12.6 volts is fully charged and a trickle charger is not the way to "charge" a battery. Trickle chargers are used to "maintain" a battery. Flooded batteries can be safely charged at at charge rates up to 20% of their AH capacity. If you have a stereo system on this boat the clock and station memory draw a small amount of current. That shouldn't kill the battery in a couple weeks but if the battery is never fully charged the discharge curve drops off quickly.

 

[Augoose]

Re: Battery issue & question

12.1 volts is NOT charged. 12.6 volts is fully charged and a trickle charger is not the way to "charge" a battery. Trickle chargers are used to "maintain" a battery. Flooded batteries can be safely charged at at charge rates up to 20% of their AH capacity. If you have a stereo system on this boat the clock and station memory draw a small amount of current. That shouldn't kill the battery in a couple weeks but if the battery is never fully charged the discharge curve drops off quickly.

Thanks for the response. I didn't mean to suggest that 12.1 volts meant it was fully charged, rather I was just mentioning that it was different than the 9 volt reading I got 15 minutes earlier when it was in the boat. However, if it was indeed 12.1 volts, wouldn't that be enough for the starter to at least begin to turn the engine over?

The "trickle" charger I am referring to is a Minnkota MK110P. I am probably incorrectly calling it a trickle charger, as its a 3 stage automatic charger. Hopefully it will work to fully charge a battery. Link here - link
Regarding the drain, the radio I have is a old one with a dial tuning knob. That will be my next troubleshooting target, then if that's not it, I'll move on to the alternator. However, I think with draining this battery three times now, its time for a new one.

Thanks

 

[RicMic]

Re: Battery issue & question

I have the same charger and its definately not a "trickle" charger, its a 10 amp charger. Take the battery to the autoparts store and have them load test it, I've had batteries with the same problem before.

 

[Silvertip]

Re: Battery issue & question

12 volts is essentially a dead battery. To prove this, attach your voltmeter and hit the key. You will see the voltage drop to zero under load.

 

[Augoose]

Re: Battery issue & question

12 volts is essentially a dead battery. To prove this, attach your voltmeter and hit the key. You will see the voltage drop to zero under load.

So that's the difference - it read 9 volts on the boat because it was under load and then 12v.1 once removed from the boat.

Thanks all for the info - I'll replace the battery, have the alternator tested, and make a point to remove and take the battery with me when I leave the boat for more than a couple of weeks at a time.