12V battery charging

Thank you for your understanding!

I wish I could say the state of my country is "civilized" right now, but sadly not.

I did notice you said voltage drops below 13.0 V while the car is in motion. (If I read your post correctly). This is a concern.

EDIT-. I think you mean acc mode shows 12.3 V. That seems okay to me.

Do you have the battery model/specifications? Is it AGM or (flooded) lead acid?

moto g(7) power ?

 

Electronic load test, then charge or replace, depending on test results.

 

With the car "on", using the dash displays? Virtually meaningless.

At the least: measure the battery voltage with a digital volt meter, first thing in the morning, with the hood popped the night before (if possible). If it's not possible to leave the hood unsecure, pop it in the morning, but go in through the passenger door, to avoid waking the car up, as much as possible.

Better: assess the battery with an electronic load tester. These must be clamped to the battery posts, check the voltage AND determine the battery's CCA (Cold Cranking Amps). While the Prius battery doesn't "crank", this measurement is still the best for determining the battery's health. These testers typically will have you set up various parameters, the battery type, the CCA spec, then you do the test, and it'll give a verdict, how viable the battery is.

In North America an example of such testers is Solar BA9. Dealerships, aftermarket retailers of batteries, usually have a pro-level tester of that ilk. The aftermarket retailers will likely run such a test for free, hoping to get your business if you do need to replace.

 

Wow, never considered a load tester, looks like these go for ~$50. This would have saved me pretty much my whole weekend angrily fuzzling at my multimeter xD

 

No. Toyota does say to disconnect before charging, but I've never done that, no problems.

Do look into smart chargers too, if car has lots of down time.

 

15 hrs per day or week should be enough to maintain a healthy 12v battery, be it AGM or flooded.

Always keep the vehicle in 'Ready' or OFF, never is accessory or standby.

 

Flooded for Prius through? I've assumed the gen ii has a harder time maintaining flooded batteries, thus AGM. Anyone tried?

 

A battery in good shape will usually show CCA well above spec. When they're getting on the CCA will start to drop, and the at-rest voltage. If (for example) rated CCA is 325, and the battery's testing at 375~400 CCA plus volts around 12.7, it's in the pink. If it's 275~300 and voltage inexorably dropping, to around 12.3~!2.4, and the tester's saying viable but recharge needed, or fail, it's time.

The tester will show this, and a verdict, either "good", "good but could use charging", or "fail". I'm paraphrasing, it's something like that. After hook up you need to enter a few stats, the rated CCA and battery "type". There's a sticker on the back clarifying which is which. I use previous Solar BA5, similar tester. Dealerships and automotive retailers will have pro-level of the same ilk, more robust, full featured and often capable of thermal printout. But prosumer like BA9 are fine for DIY'r.

 

Besides the OP? :

I'm using a $25 lawnmower battery for Prius 12v | PriusChat

Battery Replacement - Economy Method | PriusChat

 

That's "moderately" low. Coonsidering it's only 18 months old I would try charging first. Even you ultimately need to replace, it's worth a try, and an appropriate smart charger, used regularly, would be good for maintaining the next battery. Look for a charger around 3.5 max rating.

 

One does not need a tender that claims to be "AGM compatible".
They are all compatible enough.

And it won't charge very fast in "ready" mode.
Not necessarily a good idea to leave it that way for 12 hours or more.

 

A smart charger will limit the current as needed, and is recommended for AGMs.

How fast is very fast, and what do you feel is a safe continuous amperage to charge at which includes "very fast" as an end goal?

Though it could've been overlooked, not sure anyone mentioned 12 hours or more

 

No, I'm not taking the troll bait.

Charging a battery "very fast" is NOT a good thing to do.
Toyota recommends no more than 4 amps, I think......but a bit more than that should be OK for a short time.

A completely dead (or almost so) 12 V car battery might take 12 hours or more to charge at the recommended 4 amps max.

 

The car is using the battery in the process of displaying it's "diagnostics", in short: it's less than useless: it's only displaying volts (not testing Cold Cranking Amps), and it's drawing down the volts in the process of measuring them.