12v Battery Is Discharging, Re-Charge Now !

Well, for 12.7v, I can get from 12.49v by simply driving ~1 hour. I just did than last Sat. I drove total 42.2 miles on last Sat (2002-06-27) with several stops for running weekly errands.

 

Well, PRIME or not, driving at least once a week for about 1 hour is what I think is the minimal maintenance for the 12v battery. I have let it go longer. On PRIME if I let it go 2 weeks without driving, the 12v battery SoC drops down to ~12.4v. The lowest I let it drop was 12.37v.

 

Reading posts starting back in 2009 when I joined, I would occasionally but not often see posts about 12V batteries going low but it was usually due to long vacations with the car parked somewhere, etc. These complaints mostly became more prevalent to the mainstream owners with the lock down and the extreme lack of driving. Even those of us with Primes purchased back in 2017 were not having a "big" 12V battery problem with normal driving. Under normal times, I don't believe it is a huge problem that requires a huge notification on the part of Toyota other than a best practices footnote in the manual. What car manufacturer could have foreseen this?

 

a healthy battery ought to be able to withstand 6-8 weeks of being idle. the fraw is to high when off, toyota should offer a menu to turn certain functions off, a la 'vacation mode'.

 

i realize it's the most high tech car they make, but i would like to know what all it is powering that is so important.

 

OK, three weeks from the last external charge-up. I have been driving about once a week for 40 miles, but still today is the day I have to charge-up again.

 

I just checked my 12 volt and it's right at 60% 12.18v - Where have I been? The cars been sitting for about 6 hours and I woke it up while doing my initial check. So my multimeter is calibrated to the initial reading, whatever the resolution of the meter actually is.
I have a bunch of multimeters and the accuracy can be different between them by as much as 3 or 4 tenths of a volt, unless the meters battery(ies) are low.

 

2 hours after initial read above I get 12.31
I kept the leads connected for about a minute as the voltage rose to 12.35
I'll try to get another read before the prime is woken up.

 

290 KM trip 2 days ago, today I'm at 12.34. My only hope is the meter is wrong.

 

You'll get more definitive diagnosis with an electronic load tester. They're a little pricey, around $60~80, for a prosumer level tester, for personal use. Stores selling automotive batteries often have a pro-level tester, and will likely test for free. Dealerships too, but they'll maybe charge a diagnostic fee. I'm using a Solar BA5, getting dated but still works.

 

@bisco vaction mode in gen2 Prime? imagine all the experiments we could do with vacation mide during normal driving. lol

 

The 12v battery SoC this morning was 12.38v. I hooked it up with the charger. It seems, with average 10miles/day driving, I need to charge the 12v battery every 3 weeks.

 

Rob,
I have a related question. We need to leave my 2014 Prius four for several months without it being driven. I have done this with a non-hybrid by installing a battery cut off switch which stops the slight drain when the cars aren’t used. How can I do that with my Prius?
Is there a way to disconnect the 12 volt under the hood? I’m afraid that if I disconnect at the battery and close the car I won’t be able to open it.
Thanks, Aspalt43.

 

you can disconnect at the battery, and put a thick towel under the hatch. if mice are a concern, you can put 12 volts to the jump point under the hood when you get back, then pop the hatch.
if all else fails, practice crawling in the back and opening the hatch manually now.

 

Yes, as Bisco says. You should be able to open the driver door using the metal key, then open the rear passenger door and then thru the door, reach the cut-off switch to switch it back on. To make this easier, I would leave the battery and the cut off switch exposed and fold the rear seat.