Battery Draining

[Grant Brown]

Thanks for reading this post.
I have a good running 1987 Merc 70 on a 1972 Glastron 16ft.
When I leave the boat for a week or two, the battery drains down so low that it won't even run the tilt. The alternator seems to be charging the battery as it has lots of power all day when using the boat. I now disconnect the battery when I'm not using it but I was wondering where the drain might be coming from? The battery is about 3 years old, and other than lights and a tach, there are no acessories on it.
How do I test with a multimeter to see how much drain?
Is there any value in installing a battery isolator?

Thanks
Grant

 

[xtraham]

Re: Battery Draining

if you have no electronics, that's normally the first sign that the battery is on it's way out,
does it die when it sits disconnected ?
check each cell with a hydrometer...

 

[rickdb1boat]

Re: Battery Draining

I'd take it to an auto parts store and have them load test it. If you have an inline or clamp-on ampmeter, you could tell if there is a drain and how much. A voltmeter will tell you nothing about drain. An isolater will only skirt the problem, not fix it.

 

[stevieray]

Re: Battery Draining

The battery is about 3 years old

Grant - I don't think I've ever gotten 3 full seasons from any marine battery - even keeping up on the charge over the winters. Sounds like it's just at the end of its life, as xtraham advised. I wouldn't even bother with the tests.

 

[mikeblas]

Re: Battery Draining

A clamp-on ammeter will be too insensitive to measure leakage current -- unless you have a really expensive lab-quality meter. If you think the battery hasn't outlived itself, then here's what I'd to do isolate the problem:

1) Detach the + battery cable.
2) Connect a ammeter between the battery's positive + post and the positive battery cable you've just disconnected.
3) Make a note of the current draw shown on the meter.
4) Pull fuses or disconnect circuit breakers until you see the current value on the ammeter drop
substantially.
5) Double-check your work by reconnecting all but the circuit you identified; the current indicated by the ammeter shouldn't rise.

The branch circuit you isolated in #4 is the one where you should start your investigation.

 

[whiteman]

Re: Battery Draining

6) Buy a new battery.

 

[Boatin Bob]

Re: Battery Draining

If you don't have an ammeter then just take a 12v bulb and substitute for the meter and follow Mike's post above, the light will come on if there is a drain on the battery and follow the rest of the steps to isolate it, if the light doesn't come on indicating no drain then most likely a bad battery.

 

[mikeblas]

Re: Battery Draining

7) Watch your new battery go down because you were too flippant to take advice.

 

[bandit86]

Re: Battery Draining

I agree with mikeblas' post. dont use a light bulb, may not light up. any cheap digital meter is good enough.