12V starter battery drained - risks of charging it?

welcome!

couple of issues. prius battery is agm. you need an appropriate smart charger to charge it properly.

even then, if it has internal damage, it will have to be replaced. 6 years is a pretty good run.

 

Try disconnecting the battery for 30 mins and then trying again.

 

Did it run out of gas?

If the car still has fuel, then the 12v battery may be too far gone for a charge to help.

If the car did run out of gas, you may have bigger problems.

 

Check the battery voltage for starters, with a digital display multimeter, and post. Due to charging it'll likely be reading higher than "real" voltage, but you've got to start somewhere. Check it at the jump point, and directly at the posts if you can. I believe it's tough to get to the battery in the c?

 

Classic symptoms of a worn out battery.
6 years is a bit past their normal life.
Get a new battery. Be sure it is charged before installing.

If you have a Pep Boys auto parts store nearby, they seem to come recommended for Prius batteries.
And a dealer will be a bit more expensive.

P.S. In a hybrid vehicle, the 12 V battery does NOT turn the starter like with a conventional car. It only boots up computers but the end result is about the same when it goes dead.

 

No you don't. Any "good" charger will work just fine.

It might only charge it to 95% capacity instead of 100 but in most applications, that is not an important difference.

 

The difference in chargers, as far as I know, is an AGM capable charger will be able to charge at slightly higher voltage rating. My older CTEK 3.3 doesn't have that, while my newer CTEK 4.3 does. Either will charge fine, just the 4.3 is maybe a bit more effective/faster.

 

put a volt meter on her, and see what comes back

 

when connecting the harness, do you connect the negative ring to the battery connector or to the bolt that is connected to the car on the negative side? thank you

 

Assuming that the battery was nearly completely drained and that your charger wasn’t putting out an extremely high charge rate: 2 hours of charging will not give the battery a significant enough charge to do much of anything. Charge it overnight, retry to start the car.
If it is still “dead” then put a multimeter on the battery terminals and if you get a reading above ~12.2 volts then you need bite the bullet and have it towed to the dealer. Someone who actually knows what they’re doing needs to look at it.
If less than ~11.9 volts, then you could try replacing it with the same type of battery Toyota put in it originally and see if that works. If not, then, once again, you need to have it towed to the dealer.