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spikelet 07-14-2013 05:46 AM

Flat battery again..and again..and again..etc.
Hi - my '06 Grand Cherokee 3.0crd keeps getting a flat battery. Cutting a long story short, it's intermittant (two or three times in a week, then months of behaving perfectly). Been checked plenty of times - not battery (healthy, holding charge), not alternator (charges ok), not blower relay, no abnormal off-key drain etc. Now, when I try to charge it, I can keep the charger plugged in for five, ten, twenty, even thirty hours and not even one of the led indicators on the charger goes out. Also, the charger gets very hot (more than is usual, I think). No appreciable difference to state of charge in battery. I boost start it, take it for a run and it's fine - for about 24 hrs, then repeat the above. Best answer I can get from anybody is that it's 'just a Jeep thing'!

Any ideas not already covered here? Thanks.

AZhiCntry 07-14-2013 12:43 PM

Re: Flat battery again..and again..and again..etc.
"Priority Start" battery saver on Amazon might help with your problem. However, if the battery has been run down as many times as you indicate it may have internal problem/short. I would have the battery load tested. If the battery charger no longer is charging the battery it has gone bad and/or the battery has internal short. The charger getting very hot indicates indicates internal resistance/short in the battery.
The veh electrical sys needs to checked out by a competent auto electrical tech.

jeepgcoman 07-14-2013 01:12 PM

Re: Flat battery again..and again..and again..etc.
How old is the battery? Who did the testing, and what methods were used to show the battery checked good? Have you had BOTH a load test and a conductance test done on the battery? With the proper tools (Load Tester and Conductance Tester) you can accurately check the condition of the battery in less than one minute. I don't regularly do the load test as, over time, it'll take it's toll on the battery, but I do a conductance test every time I change the oil.

If you are not aware, a load tester (battery should be fully charged to get an accurate test) puts a heavy load on the battery for ten seconds and if the voltage drop (during that period) goes below 9.0 volts, the battery is bad.

As a battery ages, the plate surfaces can sulfate (or shed) active material. When this happens, it adversely affects the battery's ability to perform properly. With enough sulfating, cell(s) can short out. A conductance test measures the battery's ability to produce current. Conductance is the measure of battery plate surface available in the battery. This determines how much power the battery can provide. This test can also detect cell defects, such as shorts or opens, which will obviously reduce the battery's ability to produce the proper amount of current. The battery does not need to be fully charged for this test.

Let us know what you find.

spikelet 07-15-2013 05:13 AM

Re: Flat battery again..and again..and again..etc.
Thank you both for the replies - so far, everyone who's seen the car says the battery's ok but I have to admit that I'm not sure if they've load tested it.

By the way, another symptom that always crops up just before it 'misbehaves' is that, when I first put the key in and turn on the ignition, the air blower comes on full for a second or so, then subsides to normal. I'd heard that a suspect resistor can be to blame, so I've already replaced it but this clearly hasn't cured the problem.

Do you think that a battery trickle charger/conditioner would show up any problems?

Thanks again for the input!

jeepgcoman 07-15-2013 10:34 AM

Re: Flat battery again..and again..and again..etc.
No, a trickle charger won't show anything. They're a good slow charge for an otherwise good battery though. If you're charging it for hours on end and all it does is heat up the battery and the charger, you may have a shorted cell. You didn't say how old the battery is either?? Sometimes a trickle charger will trip its internal breaker when it heats up as much as you're describing, but apparently yours is not overheating that much. Also, a bad battery will give you all kinds of strange electrical symptoms.

Bottom those tests or try a new, or known good different battery out of another vehicle. You'll then know almost immediately if that's it.

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