Ghost Battery Drain

[Bill_Diana]

Have plans to leave tomorrow, Wednesday, for a 3 week trip to Lake George, Lake Placid and Cooperstown, New York.

This morning went to start the motorhome and nothing. Not even a click. Used voltmeter on battery...completely dead. Went dead over night. Battery is only 2 months old. Took it to Sears this morning and it tested perfectly OK. Connected to motorhome and all starts just fine. Voltmeter shows 12.46 volt. One hour later the voltage drops to 11.1 volts.

Something seems to be draining on the battery. Any ideas on what to check and how to check it?

Thanks So much.

[MEXICOWANDERER]

24 minutes at 10 amps is not one forth charged. Double it and it would not be half full. Around 12.3 volts. You have described in precise detail


A

BAD

Battery

Thirty five years ago I designed batteries and I made and constructed TESTS for flooded batteries. Life cycle testing, Ampere hour qualifications for BCI, and finally pulse charge desulfation design and analysis.

This is exactly why I would rather **** down my leg than have a burger-flipper argue whether a battery is a fatality. I go to Costco not Wal-Mart, Sears, or Pep Boys.

And with this I sign-off commenting as further time will lead nowhere.

[Bill_Diana]

Roger10378 wrote:
How did Sears check the battery? To properly check they would have to charge completely which would take several hours, then let sit for an hour or so and finally check the voltage and do a load test. Any thing that they do while you wait is meaningless.

The fella at Sears did a discharge and then did a fast charge that took 24 minutes. Then he used another device that checked the cranking capacity. I believe the battery is OK and the problem was the brake lights being stuck on.

This morning after the battery was connected in the motorhome overnight, the engine started just fine. So we were able to begin our trip to Lake George as planned.

When 10 miles from our destination we got stuck in a terrible traffic delay. Due to an accident all 3 north bound lanes on I87 were shut down. We creeped for 3 3/4 hours and only traveled 4 miles.

[Roger10378]

How did Sears check the battery? To properly check they would have to charge completely which would take several hours, then let sit for an hour or so and finally check the voltage and do a load test. Any thing that they do while you wait is meaningless.

[Captain_Happy]

Had the same battery draw problem on the last Ford F53 Motor Home. Spent days going over the rig looking for battery draw. Never found it. So I just added a knife blade disconnect on the starter battery. Problem solved. No more drained battery.

[ajriding]

Brake lights on all night will do it.

Other thought is that somehow your coach battery is connected, while motor off, still to your starting battery, and that the coach battery is of low voltage and robbing your good starting battery of its voltage. Check coach battery, if it is fine then this is not the case. If so, then check the connection between the two - it will either be a solenoid (looks like a small shiny steel can), or a battery isolator (looks like an inverter or stereo amp, likely blue color). I've never seen either go bad though.

[MEXICOWANDERER]

The days of a faulty alternator draining the battery are long gone. I mean WAY gone. Say a positive rectifier shorts out, the only thing that happens is the voltage regulator USED TO turn on. Max -3 amp drain. But that ended with the SI alternator in 1985. The CS series of alternator needs a AC signal to turn on. The 2G, 3G 4G and 6G Ford Alts cannot short nor can the MOPAR it would take six shorted not open power rectifiers to even attempt a leak. Like getting four flat tires plus the spare as far a hypothetical coincidences.

[Bill_Diana]

First of all …...thanks to each of you for coming to the rescue. I've been a member here for over 17 years and continue to be amazed on how quickly members are willing to help each other. Thanks again.

I checked the alternator voltage and all seemed OK. This really had me puzzled. Then by accident I discovered what I think was causing the battery to discharge. The brake pedal was not fully returning to the up position thus the brake lights remained on.

Everything is reconnected and I'm waiting a few hours to measure the battery voltage and hopefully it remains at 12.56 volts.

Thanks again. Once again I'm a happy camper anxious to begin our 3 week journey bright and early tomorrow morning.

[Krusty]

Check the dome lamp switch on the dashboard. It should remain in the off position. Many coach builders will install their own dome lamp that has a remote switch on it. If the dash switch is left in the on position, it will turn on the relay, which will cause a small draw on the battery.

[enblethen]

Your profile does not show make, model and chassis of MH.
A bad diode in the alternator regulator could cause such a drain.
test I suggested could show this.

[MEXICOWANDERER]

I smell a rat...

Even a constant 10-amp bleed would spark like crazy and I am to believe no-one NO ONE noticed a blue and yellow mega-spark while the charged up battery was being reconnected two times by two people?

Charger up again but leave disconnected overnight. If it loses >.20 volts you have your gremlin. If the rig has a generator you have your charger options. Troubleshoot at your campsite. You'll gather 2-tons of fender squatters (neighbors) kibitzing every move you make.

[2oldman]

That's a big drain, and tough to find. I have a car that does that, not as bad, but I simply disconnect the battery if I'm stopped for more than 1 hour.

[Sam_Spade]

Bill/Diana wrote:


Something seems to be draining on the battery. Any ideas on what to check and how to check it?

12.46 is NOT fully charged.

You often can not find out what the real problem IS in just a couple of hours.

First, you need to fully charge the battery.
And then disconnect it and monitor the voltage for a few hours......because even a new battery can go bad.

Since this is the "starting battery" (AKA chassis battery), the most common causes are a door left ajar or a dome light left on.

More information is needed about the make and model to get specific advice.

You NEED a multi-meter to properly test.

P.S. I suggest that it would NOT be a good idea to leave on a trip tomorrow......unless you find out for sure what the problem IS.

[enblethen]

First thought would be bad alternator
Put meter on battery and get good reading.
Start MH and retake reading. Should be 13.5-14.4 volts.
Verify connections on battery cables. Verify that the ground to the frame is good.