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Discussion Starter · #1 ·
The original brand new car battery was replaced by a new genuine Honda battery 17 months ago. About a couple of weeks ago after a fews days (5-7 days) of no usage, the battery was completely dead, in the past we have left the car in the garage for 2+ weeks without any problem with the battery. After that event, I fully charged the battery and used the car for a couple of days with no problem, then the car sat in the garage for 5 days and the battery was fully dead again.

This time I checked the current at the battery with the car idle and was 0.09 A = 90 mA, I think it should be around 50 mA, so it is almost double than what it should be. Then I checked the voltage at every single fuse in the 3 fuse boxes, 2 under the hood and one in the cabin. Everything was 0.000V.

I am getting to the point that the only candidate is the battery itself, weird that it failed so soon, but honestly I don't know what else it could be.

The car has Honda Care and the battery is under Honda warranty as well, so taking it to the dealership for them to diagnose. Not a fan of that because they will usually fix one thing and break something else.

Do you have any suggestion on what else I could do to troubleshoot the problem? Thank you

NOTE: The car has 29,200 miles on it.
 

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So I noticed, after reading a few similar threads, that there may be a higher parasitic load when the car is parked with the key in the ignition switch. Was yours parked with key in the ignition by chance? Key is off, but key is still in the switch.

The workshop manual has a pretty detailed description of the steps needed to get a realistic measurement. Steps include setting the alarm and some related hood-open and key out IIRC. I'd have to go dig again. Most parked-in-the-garage cases don't have the hood open though so some doesn't apply.

Many, like us, are finding that we aren't using the car as often as we did prior to the pandemic. Ours normally sits by now with a maintainer on it anyway, and another summer car comes out for the regular duty. Consider adding a maintainer to the storage protocol if the car will be sitting more than a few days.

In the meanwhile, take advantage of the Honda battery and the Honda Care contract you invested in. They will fix it or tell you what's happening, and maybe siphon some of your invested money back though your local economy. Let the service salesman know that you'd like a detailed report of the findings and fix. Then share that info back here so the rest of us can learn.
 

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Discussion Starter · #3 · (Edited)
So I noticed, after reading a few similar threads, that there may be a higher parasitic load when the car is parked with the key in the ignition switch. Was yours parked with key in the ignition by chance? Key is off, but key is still in the switch.

The workshop manual has a pretty detailed description of the steps needed to get a realistic measurement. Steps include setting the alarm and some related hood-open and key out IIRC. I'd have to go dig again. Most parked-in-the-garage cases don't have the hood open though so some doesn't apply.

Many, like us, are finding that we aren't using the car as often as we did prior to the pandemic. Ours normally sits by now with a maintainer on it anyway, and another summer car comes out for the regular duty. Consider adding a maintainer to the storage protocol if the car will be sitting more than a few days.

In the meanwhile, take advantage of the Honda battery and the Honda Care contract you invested in. They will fix it or tell you what's happening, and maybe siphon some of your invested money back though your local economy. Let the service salesman know that you'd like a detailed report of the findings and fix. Then share that info back here so the rest of us can learn.
Hi Bob, thanks for the information, the car keys were not in the ignition. Yesterday I fully charged the battery (again, third time) and started measuring the battery voltage, the conditions are: all doors closed, no keys in the ignition, nothing connected to the car and the hood open (for measurement), the results so far are:

06/03/2020 07:00PM = 13.00V
06/04/2020 07:00AM = 12.74V (12 hours later)

That means in 12 hours lost 0.26V, at this rate it will be fully discharged in 2 days.
 

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When you charge the battery as you did, it retains a "surface" charge on it for a while. No idea where the term came from or what the actual cause is, but it's close to as old as I am I'm sure. The common guidance is to let the battery settle for a bit after charging is complete before you take a reading, so whatever "surface" charge is left has a chance to level out.

Meanwhile, the Pilot, especially with higher trim, leaves some of the entertainment stack powered on shutdown. Valid measurements of parasitic drain need some time after key-out and last door close. 5 Minutes should be plenty, so the system has a chance to completely power down.

A typical at-rest fully-charged wet-cell battery will present 12.6-12.7 terminal volts. Your 12-hour number looks great, actually. Meanwhile, the most accurate test of parasitic load actually involves a measurement. There are a few clamp-on DC ammeters that will give you a reliable reading at the tens-of-milliamps levels the cars typically bleed battery current. I have a really handy one, but it's so sensitive that it needs to be zero'd several times at a place very close to where you'll take measurements, so stray magnetic fields in the area don't cause false reading. The first reading is for total drain, and that's done on the ground cable. If that static reading is high, then the fun starts as you try to isolate circuits and see what's actually leaking.
 

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Discussion Starter · #5 ·
The every 12 hours voltage measurements are:

06/03/2020 07:00PM = 13.00V
06/04/2020 07:00AM = 12.74V (0.26V decrease)
06/04/2020 07:00PM = 12.62V (0.12V decrease)
06/05/2020 07:00AM = 12.54V (0.08V decrease)

At this rate the battery will be dead very soon.
 

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If there has been no other service done involving electrical parts, no PCM updates, etc, AND the only difference was a new battery, then I'd focus on the battery. If the dealer battery inventory doesn't rotate often, then it may have been an old "new" battery with compromised capacity, or had internal plate damage during shipping, manufacture defect, etc. It happens. Assuming a fresh good battery has at least 60Ah of reserve capacity, and the 90mA draw is representative of the sleeping system draw, then you'd get about 28 days before the battery voltage dropped below 10.5 and would be considered "flat" and would struggle to turn the starter. As Bob mentioned, the battery terminal voltage drop rate isn't a reliable method to predict discharge rate.
 

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Discussion Starter · #7 ·
I've come to the same conclusion, it has to be a defective battery.

Nothing has been changed, upgraded or modified anywhere in the car; electrical and non electrical (apart from new tires) since the battery was replaced.

Today I connected a DC Amp Clamp Meter to the cable that connects the batterie's negative terminal to the chassis of the car, and the amount of current is in the range of 40 to 60mA, in line with the specs and standard information.

I did the same test on a 2020 Toyota Tacoma and the results were very similar in the 50mA range.
 

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Just grabbed a reading to be sure:

136893
 

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Just out of curiosity, how accurate are those 100A and 400A rated current clamps when you’re measuring in the mA range?
 

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My UNi-T 210E is accurate within a few milliamps over 10 minutes on the 2A scale, if I take care in zeroing near the wire to be clamped. Good enough for what I do.
 

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Discussion Starter · #12 ·
I use mine in the 40A range, I can't tell about accuracy because I just purchased it
 

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Thanks for the info. I’m going to have to add one of these to my debug toolkit.
 

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My UNi-T 210E is accurate within a few milliamps over 10 minutes on the 2A scale, if I take care in zeroing near the wire to be clamped. Good enough for what I do.
I use the same one for very light load detection. Picture of the display on post 8. As AVC shares, it's so sensitive it gets zero'd a few times next the wire you are testing before actually clamping around the wire. The meter was <$40 a few years ago when I bought it. A brown truck deleivered it in a smiley box.
 
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