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Discussion Starter · #1 ·
2012 EXL with 110,000 miles. The CARFAX says the battery was replaced at 33,700 at a dealership in 11-2014 and battery "serviced" last at about 71,000 miles in 12-2016.

We just recently bought it at about 108,500 miles. Installed VCM Tuner II soon after.

Had a bad AC Clutch relay on our Odyssey and it literally killed the battery completely dead overnight, sometimes within a couple hours. To where the battery was destroyed and would not even take a charge at all. This is not like that, but I don't know if all relay failures cause the same pattern of symptoms.

The battery dies when the car sits overnight, not always but sometimes in the morning it'll be dead. It seems like after a day when the car has not been driven is when it happens, twice now in about 2 weeks. The battery will take a charge from a trickle charger easily and immediately and then it's fine again. Advance auto tested the battery and alternator and said both are good, but he said he couldn't tell me if the battery is slowly losing charge.

The battery shows 14.3 V when idling and 12.7 V with the car off. I did a parasitic draw test with multimeter at 10A and it showed .05-.06 I pulled the fuse from the VCM Tuner II and it dropped to .04-.05. I then pushed the hood latch over and now it reads .02-.03. Pulling the AC Clutch relay out did not cause any further drop but maybe it would not be expected to? I don't know if pulling a relay works the same as pulling a fuse as far as observing a drop in the battery draw?

The AC works fine and has not blown out the refrigerant, although the AC clutch does seem to make a bit of a humming noise when it kicks on at idle. Not sure if that could be caused by a bad relay or not, or maybe it's normal.

Right now it's sitting with the negative terminal disconnected. I was going to just let it sit that way until tomorrow morning and then see if the battery was weak, but maybe someone smarter than me here has another suggestion to diagnose a bit quicker? Could it still be the relay? Or maybe the battery is just old and losing charge when not driven daily?

Thanks in advance!
 

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The 0.040 Amps parasitic drain is not enough to kill the battery overnight. The battery has a new capacity of somewhere in the neighborhood of 65 Amp/hours, so your 0.040 (40 milliamps or forty thousandths of an Amp) means the battery is losing 0.06 percent of it's capacity every hour it sits, or the inverse-- it will take somewhere north of 1500 hours to drain that new battery.

Without knowing exactly the life the battery has lived, remember that 6 years is a good expected life for a wet-cell battery in a car. I'd be looking a a new battery right about now. I'd charge it off the car and check the specific gravity in the cells, but then replace it anyway if there's any question of its health. But that's me. I hate getting stranded by stupid stuff.
 

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The battery shows 14.3 V when idling and 12.7 V with the car off.
What is the voltage drop while actually cranking the engine? If going below 10 volts while cranking the battery is not healthy. 6 years? Time to replace.
 

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I agree with @dr bob , replace the battery. Sometimes we can drive ourself crazy when you can just replace a part and be done.
 

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Discussion Starter · #5 ·
The battery shows 14.3 V when idling and 12.7 V with the car off.
What is the voltage drop while actually cranking the engine? If going below 10 volts while cranking the battery is not healthy. 6 years? Time to replace.
Thanks for the reminder, I completely neglected to check that. Just checked and it dropped down to about 8 Volts while cranking. New battery will be going in today.
 
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