'04 Prius Bad 12v Battery?

Have a '04 prius with 150k miles on it. Replaced the 12v battery back in February, since the car sat for the winter. Replacement battery was an Exide AGM I found in town. Has been used a daily driver for myself, and occasionally the wife. Drove home from work (about 6 miles) without any issues. Went to move the car and found that nothing was powering on. No red immobilizer light, no headlights or dome lights. Hooked up the booster I have (has polarity protection, but was correctly hooked up). ICE fired up and was the car was pulled into the garage. Cannot use the MFD to check the health of the 12v as that is out, and the replacement hasn't shown up yet. Pulled out the multi meter and checked the voltage at the jumper points, and got 3V. Assumed the auxiliary battery is bad. Jumped the car again to move it out of the way for the wife, and the ICE did not start, and got a red triangle. Nothing showed up on the code reader, but was able to limp in electric mode out of the way of the garage. Started pulling the auxiliary battery, but decided to check it out once the negative disconnected from the chassis. Battery was shown up at 12.7v. Connected back to the car, and 3v. Started checking fuses, the current probes I have can't read lower than 1A, but I get my clip on ammeter back tomorrow. Threw the battery onto the smart charger I have, and it kicked off in about ten minutes. So I'm left to believe the auxiliary battery is good.

Should I try tracking down a potential short, or just swap out the auxiliary battery?

 

JC,

As I previously said, the battery is three months old. It also was reasonably fresh when I bought it (6 months according to the sticker). I did let the battery rest unconnected and showed 12.7v. Reconnected to the car and dropped to 9v. Waited a half hour (no keys to wake any of the ecus ) and dropped to 3v. So I'm guessing the battery has gone bad.

Patrick,

I thought of that as well. Checked all the cables I can get to and all measure around 20~25 milliohms, so the cables are good. Ground screw had a little rust, which I cleaned and put a little dielectric grease on. This connection measured 15 milliohms. I'm going to pull the battery and swap it. It should still be under warranty so at least it will be cheap.

If anyone has any other suggestions, I'm willing to give them a shot.

 

Just providing an update. Replaced the battery under warranty. The car starts now. Went ahead and checked current draws. I'm assuming the 50mA on the small 18 gauge wire and ground is just normal draw. What I find strange is the 500mA draw on the heavier positive wire. It seems to me this is going back to the brake box next to the battery, but I don't have to a way to check that. Is this something else to be concerned with?

Also, with the car in "ready" the battery is at 14v so I am assuming the inverter or whatever alternator alternative is in the vehicle is working correctly. After sitting overnight, the aux battery is at 12.1~12.4 VDC. Is there anything else I should check? I just don't want to play battery swap every three months.

Thanks for the suggestions.

 

Patrick,

Any suggestion on which relays to look at? Since this is measured only on the high voltage side (assumed since this is the larger cable), I would assume those relays would not be up front. I do not have the manual for the car to find the relay layout.

 

Sorry for the confusion, should have said high current side. When I measure on the smaller wire, I get roughly 25 ~ 50 mA. Depends on how long I wait. But the larger one stays at 450 ~ 500 mA.

I've checked the relays in the horizontal box at the windshield, and about a 1/4 in the vertical box by the fender. I'll have to try tapping on the ones I cannot remove. Is there anything specific for the ones under the instrument panel? I found some info for that box, but nothing special. The trim panel should be easy to remove, I'm assuming.

 

Just to provide an update, checked more relays. The ones by the driver side door were fun. But I believe the relay for the IG1 is starting to go. I pulled it, and checked current and it dropped by 150 mA. Put it back in, and checked again, and with all doors closed the current dropped to 20 mA. Sadly, I deleted the part number out of my phone, so I'll have to pull the trim panel off again to get it. Unless there is a kind soul who knows the number, since my googling is not finding a part number. One last question, is there anything better about the Toyota relay versus one from Napa? I assume they are coming from the same place, just with different silk screening.

Thanks for all the help.

 

I looked up the original vendor Denso and found their stock number. So a little work and found the equivalent part for $15 on amazon. Good enough for me. Thanks again for the help.

 

Sorry for the long reply.

For the IG1 relay, the Denso part number was 567-0003. I got mine from amazon

For the other somewhat standard relays for my prius, there was this one 567-0001 and 567-0002.