Need some help with my V12 Auxiliary battery

Any cheap trickle charger 2 amps or less overnight should bring it back up. If it doesn't charge up spend the money for the new OEM Toyota battery and don't worry about it again for 6-8 years.

If you call a couple Toyota dealers you should be able to get one for less than $200. The aftermarkets are not as good as the OEM Toyota IMO. I buy about 10 per month from my local dealer. I have tried all of the aftermarkets and get the best results with OEM.

 

Inexpensive battery maintainer, Die-Hard (Sears) 28.71219, I think I paid $19 for mine. Whenever car is garaged, the maintainer is connected (just in case) Welcome to PriusChat!!!

 

Amazon has a nice ac delco prius battery, around $120

 

I picked up a Bosch for $140 the other day, came with a 4 year replacement warranty. Put it on the little G750 charger for a day and it came up to a nice 13.6V. I wouldn't buy any special chargers; the charging specs on the battery are suited for normal chargers.

 

Looks like a good choice, albeit the amperage is a bit low. I would go for the 3.5 amp. Check the owners manual, but I believe it recommends 3.5 amp max (page 315).

FWIW, I use a couple of CTEK: a 3.3 and 4.3 (both the name and the amperage). You want a "smart" charger, assessing the state of charge as it goes, runs through a regimen, and when wrapped up can be left on indefinitely if needed, as a maintainer.

 

If cost is a concern, I've read of others using batteries that cost under $40.

Or if you are looking for something that is less expensive and on par with the OEM option: Fitting mobility 12volt AGM battery. | PriusChat

 

Given that it is driven daily......IF the voltage measured at the battery while the car is ON (ready to drive mode) is 13 V or above.......then just replace your failing battery.

There is no good reason to believe that ANY external charger will keep the old battery alive longer than the onboard charging system will........unless maybe you could plug it in every night and then you are just postponing the pain.

 

isn't the prius able to run without the 12v?

 

Run? ...not sure; get to Ready? ...doubt it!

 

right. won't go ready, but i thought if you were driving, it wouldn't shut down. i could be mistaken though.

 

It seems likely that the hybrid system's 12v charging system would take over and keep the hv relay closed and the computer running. But then when you stop, you'd be stuck. Best to bite the bullet and get a new battery. How much you spend depends on how soon you plan to get rear ended at a traffic light.

 

sounds like a plan, please let us know if anything goes right. all the best!

 

When you say "under load" I assume that's when the car is not in ready mode?

If it's low in ready mode your inverter is not charging it.
You should pretty much have normal voltage in ready mode as the inverter will pull off the traction battery to keep the auxiliary up and even kick on the engine if necessary.

If you're in simple auxiliary mode then it's just your battery.

 

That 12V battery might be a bit weak, but it definitely isn't what caused the loss of power while driving!

You need to start looking into other causes, and first on the list would be inverter coolant pump failure. Also, check all your fluid levels.