12V battery maintenance for dummies when gone for weeks

@Mendel Leisk and @Pdog808 thank you!

@bisco thanks. You're right. When I pulled into Auto Zone today, an employee had just finished checking someone's battery. He then helped me. Walking in, I saw a different employee checking someone else's car. lol. It's battery day at Auto Zone.

I had intended to buy the Noco Genius 1 there, but the website was wrong (they didn't have one in stock) so I've ordered that and the Solar BA9 charger from Amazon and will get them tomorrow. I'm curious now. The Auto Zone battery tester didn't show CCA but said my charge is now 32%. I didn't drive at all last week. My normal driving is not helping (mostly short trips around town) but I'm surprised this is even lower than the 61% charge and 73 CCA when the car sat for 6 weeks. (the AAA display, photo above. BTW, the AAA guy did not connect to the battery directly but under the hood. And his display shows the battery specs at 350 CCA, not 285 CCA).

I had a 2006 Prius (and other cars) and never had this problem, so this is frustrating. Is there a definitive list of things to be mindful of related to the parasitic drain? I read some of long chat thread, which is a discussion (key fob bad or not?), but I'm wondering if someone compiled a definite list. thanks

 

@Mendel Leisk you're right. Typo. BA9 tester. Gorgeous photo! BC is so beautiful!

@BiomedO1 when the AAA display showed 73 CCA it also said that battery needed to be replaced. But it claimed 61% SoC. Thanks for mentioning the faraday boxes. I dug out my old Mission Darkness bag (which apparently no longer works) and ordered a new box. (the fobs are now sitting in a ziplock bag inside an olde school coffee percolator. works! lol)

I made an appointment at the Toyota dealer tomorrow and briefly spoke to a service agent. He said that cars that are rarely driven, especially PIP, have problems holding a charge. But they'll check it out. I'm going to ask them to do a full charge and see if it will hold. I'll also ask about parasitic draws, maybe they can check for that. Anything else that you think I might want to ask? Below is my news/actions from Friday.

On Friday my package from Amazon arrived, the NOCO Genius 1 and a TopDon tester (the Solar BA9 won't come until Sunday so I thought I'd start with this and return the one I don't want). Findings:
1) 2pm first check, the 12V charge is 0, CCA 229 (Thurs @ 4pm AutoZone tester show SoC 32% and CCA "passed", whatever that means)
2) 3pm driving for 35 minutes, the charge is 20%, CCA 176
3) 7 pm a few hours later, charge is 0, CCA 182
4) 9 pm charge is 0 and CCA is 260. After 7, I drove 10 minutes. Parked for an hour while I did something. Then I drove 45 minutes on a freeway and checked it again. I can't believe that the charge would be 0 after driving so long.

Possible problem: Between 3 and 6ish I connected the NOCO Genius 1. I made a mistake. I couldn't figure out which type of battery it is (not in the manual) so I googled and a chatbot said it is a flooded lead-acid type. (it referenced priuschat and larryhmillertoyota.com). Since then, I looked at the label on the battery itself and saw "345LN1-MF" which I think means it's an AGM battery. So I charged the battery using flooded 12V mode instead of 12V AGM mode, 1 amp for about three hours. oops. Not sure if I wrecked the battery completely. (?) It wasn't holding a charge though on Thursday night before I intervened. Thanks for your help!

 

@Mendel Leisk, thanks for all this info especially charging AGM in regular mode. When I googled about that, info was all over the map. I did enter the 285 CCA manually on the Topdon, per the label on my battery (photo posted beneath the AutoZone tester on Thursday). FWIW, when the dealer charged it after the Thanksgiving dead battery incident, they measured 286 CCC for the 285 rated battery. (so higher but just barely)

The voltage number appears on the Topdon when you first connect it to the battery, there's like a "home page" with that number. But it kept fluctuating between slightly different numbers. Maybe it's hard for the device to function when the charge is so low.

Do you know, are they any magic words to get the dealer to replace the battery? It's one year old. When I reviewed the warranty booklet, it seems like it falls into the 3-year range. The service advisers keep saying batteries do this if you don't drive them often, but I'd had similar driving patterns with the 2006 prius for at least the past 5 years without incident (I replaced the 12V once in the 19 years I had it, maybe 12-13 years in. I can't remember, but definitely not in the last years when I was not driving much, including during the pandemic!)

 

@Brian1954 good to know. thanks. I'm taking it to the dealer tomorrow, so I'll see what happens there. But thanks for this tip. I may upgrade to the NOCO 10.

 

@BiomedO1 thanks. Yeah, I wondered how much power the testers were drawing out of the ailing battery. But I was surprised that I had the 1 amp charger on there for 3 hours and the SoC went from 20% to 0%. I made a point to close the hatch (so the dome light wasn't on).

I guess the lack of driving is the issue but I didn't have this problem with my 2006 Prius, and I had similar driving patterns probably the last 5 years. So I guess this means for me....that I must have really damaged the battery letting it sit for 6 weeks (with a friend driving it around the block once) and now my limited driving is becoming more of an issue.