Battery unable to hold charge -- 2008 Prius

Get familiar with disconnecting the 12v bat, and not locking yourself out of the car/trunk. Charge the 12 v bat overnight with it disconnected. Get a cheap digital voltmeter so you can check the 12 bat before, during, and after charging it.

Be careful trying to "start" your car too many times or you'll deplete the HV bat (which is what starts the engine) and you'll have to build a grid charger to charge the HV bat.

 

That's well over the 3.5 amp limit recommended in owner's manual. I'd recommend CTEK 5, though pricey. It's charging spec is 4.3 amp, at least close.



Just my 2 cents: fugedabout AAA, warranties and so on. Read up about automotive 12 volts, learn how to maintain them, a lot less grief.

 

get a foxsur charger from amazon, a lot cheaper.

 

as Bill Clinton said what do you mean by "it"

 

If the AAA guy put a voltmeter on the current 12V and it read <10V, or something so low that he declared it "dead", you should stop trying to resuscitate that corpse and move on. Get a new 12V, verify that it is reasonably charged (over 12.5V) before leaving the store, and install it. Then hopefully there is enough left in the pack to start the motor, and you can let the car sit for a while to charge the pack (and to a lesser extent, the 12V).

 

From everything you have described the most like scenario is that the car sat for a long time unused. The power draw from the car when it is off (some stuff is still live) drains the 12V over several weeks and if it discharges too far it damages the battery. This was a very common problem during the pandemic. There is nothing you can do to fix this AGM battery once that happens, the battery must be replaced. The observation that the car craps out once it is off is also consistent with a really bad 12V battery - when the inverter shuts down only the 12V is left to provide power, and if it cannot do so, the electronics in the car will go haywire.

If you really think it isn't bad, then remove the 12V from the car, take it to a car parts store and have them test it. Since it is probably very discharged they will need to charge it for a while (at least half an hour) before they can run a definitive test. It will probably fail that test. If money is a problem find somebody at school who is into cars and have them help, they may already have the tools to do the same thing. If there is power near enough to the car it can be charged in situ. Since things are a little iffy in your case, it might be best to detach the ground lead and charge the battery at its posts, just on the off chance there is something else going on in the electrical system. Normally it is OK to charge the battery from the jump post under the hood, with the caveat that the maximum charging current should be less than 4A.

Or...

Just get a new battery. Call around to Toyota dealerships and see what they charge, or get the one from Walmart, which has been getting good reviews and will cost less. The auto parts stores all sell a version but they may not have one in stock. Once the new battery is in the car may just work. If not, at least you know it isn't the 12V. Be aware that the first time you try to start the car after changing the battery it may fail to do so or it might throw a code (I don't recall which). Just try it again and it should start normally. Assuming there isn't some other problem. And there might be, because all the attempts to start the motor may have drained the pack too much to start the motor.

 

The only place to get a battery installed is the dealership or a mechanic

if the car won’t start after you have charged the battery (try not to get confused between the 12 volt battery and the hybrid battery)
And you’re not keen on buying a new one unless you absolutely have to, get a free load test at auto zone for a definitive result.
Try to put out of your mind anything the triple a guy said

 

got to have your priorities

 

Sounds right to me.

As you starting to see these are pretty complex cars. It’s easy to spend a ton of money trying to fix them. Many of us have learned to do some things ourselves and save a fair amount, but it’s a steep learning curve. Good luck to ya!!

 

The main issue I've found with Toyota batteries is the abysmal hold-down bracket: it's an odd, proprietary design, completely intolerant of any variation in height. Aftermarket batteries that are just 1/16" different, you need to shim under the battery, or add washers under the bracket, depending if the height is less or more. About on par with their scissor jack design...