12v Battery Is Discharging, Re-Charge Now !

While I was checking my PRIME's less than 1 year old 12v battery, I also checked our two other car batteries. Both cars are hybrid and 12v is not used for starting engine, I think. One is OEM Nissan battery at least 6 years old, other is aftermarket EXIDE battery less than 3 years old. All three batteries including my PRIME's OEM battery showed 12.42v-12.47v on battery tester reading with 70-78% health initially. At least on my battery tester, anything above 12.4v seems to be fine.

 

Day 2. After 36 hours, the battery is now 12.74v, but still 100%. In 24 hours period, it discharged 0.15v. If the discharge rate is constant, then after 7days, the projected losses will total 1.05v. Starting from the full charge of 13.06v, it will be down to 12.01v or 50% in one week.

 

wow, if this is typical, toyota has really dropped the ball on 12v battery management. after 15 years of 12v problems, i can't believe they've made it even worse. especially after moving the battery to the engine compartment, where they coud have installed a beefier unit.

 

Is the flooded acid battery self-discharge rate affected by temperature? It was low 20s this morning.

 

Yes, it will be faster at higher temps.

 

OK, that means in my local self-discharge is already lower than hotter places.

 

i'm surprised we haven't seen more complaints. there have been tons of gen2 and 3 covid 12 volts

 

After 1 week, I will see what 30 miles drive will do to the battery. That's what I have been doing last 4 weeks, and I did not have problem.

 

I don't know the answer. But since it dose not need to crank the engine, I would think it can be lower than regular car.

 

Here is reading 52 hours after a full charge. It is now reading 12.72v. In the last 24 hours, the discharge was from 12.81v to 12.72v, a total of 0.09v.

 

I remember on our Prius V, when the battery died, it was in the low 10 V range that would not start the car. Though I did get five years out of the12 V battery.

 

Agreed. My Primes almost brand new battery that was only driven for two weeks after purchase on March 1st and driven only once a week ~30 miles after mid-March was measuring 12.38v before the full charge. If it did lose 0.1v each day, after a week, it could go down to ~11.7v which is still OK charge for starting PRIME, but if it goes longer periods, say a few months, it may not hold enough charge to start the car.

 

from past history, the resting voltage is not a good indicator of a weak battery. it seems that the voltage under load can vary, battery to battery with the same resting voltage. and that's what makes testing tricky.

in older cars, there also seems to be an element of the cars internals also varying from car to car, putting more or less load on the batteries.

 

Today my 2020 Prius Prime was @ 12.24 with a multimeter. This thread has inspired me to check on a regular basis. Even though I've had the vehicle since end of Jan I've only travelled 300 KM, difficult to go anywhere given the virus conditions. Spreadsheet initiated.

 

wow

 

Looking at CTEK, Nocco, and Battery Tender chargers. Any recommendations?

 

Yeah, but electronics can be picky about electricity 'quality'.

Also climate has an effect. Along with how long the car sat on the dealer's back lot.