Batteries draining after sitting a week.

[Henner]

I have two new Interstate marine batteries hooked to a perko. The last 2 weeks when i get to the lake on Friday both batteries are almost dead. (Won't crank engine over) I can put both them on the charger and they charge right back up and boat starts fine on either battery every day afterwards, until it sits Monday through Friday then rinse and repeat. What could be draining the batteries with the Perko off, this has just started the last few weeks and nothing has been changed or touched.

Thanks for the input.

[CJD]

There are 2 possibilities. Either you have a drain or they are not fully charging.

Check the charge by using a voltmeter at the batteries. You should see 12.6v with everything off, and that will jump to 13.5-14.4 volts with the engine running.

If that checks, then disconnect the battery lead and use an ammeter between the lead and the battery. With everything off, you should not see more than .02 amps. If the drain is .5 amp or more, you have to pull fuses till you see where the drain is coming from.

[lively]

What he said . Something is pulling them dead or they are not fully charged . I always charge them on the bench and then watch them with my voltmeter to see where they level off at . Should be about 12.6 vdc


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[michael hunter]

With the perco switch off both battery's should be isolated from the boat. Check the wiring at the battery's and make sure nothing is wired around the perco switch. Have the batterys tested one or both may have a short internally.

[Wylietunes]

There should not be any electrical loads wired directly to either battery B+ post, except the auto bilge. So if the switch is off when the boat is out of use, there should not be any draws. Even if there was a draw on one, the other should remain charged, unless the switch is left in the BOTH position. So if the switch if OFF when the boat is stored, you need to A) make sure the batteries have a sufficient charge when you are done using it. B) make sure the alternator has ample output, if not, you are back at (A) with low batteries when putting away. Its rare to have what appears to be a good battery, one thats able to reached a full charge, but bleeds down in a week. In most cases, you will find that the battery is not able to reach a full charge, prior to the storage period.

[Henner]

I put them both on chargers last night. I am going to leave them on for 24 hours and check them in a couple days and see what volts they are at.

[CJD]

I am sure you are getting a full charge on the house charger. I am just not so certain you are getting a full charge in the boat. It may just take it a couple days for them to run down following the full house charge. You will have to check the voltage at the batteries with the engine running. If it is less than 13.5v, then you are not getting a good charge on the boat.


Also, the Mike's are correct...there should be nothing connected directly to the batteries before the perco...but you can never be sure with older equipment. A lot of PO's don't know the rules of good electrical work.

[Blackntan90]

Good info everybody! Oh 1 more thing to check is nice clean grounds....been bit by that one before!

[Henner]

Sorry for the dumb question where is the fuse box on a 90 comp?

[michael hunter]

Under the dash.

[Hagman]

A faulty diode in the alternator will draw power for the battery . Easy check. With the motor cold the alternator should also be cold also.

[td in nc]

Would low water level in the battery impact this issue? May be worth making sure there is enough water in the battery.

[Wylietunes]

TD makes a great point. Checking the batteries fluid level should be done a couple times a season, depending on uses, charging and how dry the climate is. Low cell levels will impact its ability to reach a full charge, this reduce its performance.

[SquamInboards]

While low fluid level will of course affect battery performance, I have not had to add fluid to a battery, any battery, in probably 15 years. That's just my experience...

[Henner]

Ok charged them overnight Monday and checked them both this morning after sitting 3 days and both were at 13.2vdc with the perko off.