My Prius won't start, but full battery.

well, i think you should start by measuring the battery voltage with a dvm, and not trusting the charger.

 

sure, you can pick one up at any hardware store, sears, amazon, etc. digital volt meter, ten dollars.

the best way to test is to pop your hood at night when you're done driving. in the morning, before opening the doors (which activate the electronics and affect battery voltage) open the hood and hook the volt meter to the 12v positive in the fuse box and a negative ground point. if it reads 12.5 or less, that's your problem.

the problem with a lot of battery chargers is that they can't tell you whether the battery is good or bad, just that it's no longer taking a charge.

 

you can jump start it, but don't shut it off until you get home.

a new battery should be around 13.0 volts. as they age, 12.5 or 6 is the bottom limit. my 3 year old battery reads 12.7, but things can happen in the battery that can make the static reading unreliable. one issue for the prius battery is that it's very small, and running it down by leaving a door open/light on can kill it dead. then you have to get into turning on the headlights and watching the reading etc.

you don't want to test it after the car has been on, because you get a false reading from a surface charge from the car which takes at least a few hours to dissipate. i wish it were simpler, sorry.

btw, can't you go back to the seller for satisfaction?

 

i wish you all the best my friend. i trust my children to make at least as many mistakes as i did. your hearts in the right place, that's all the matters. tell them to call me if it doesn't work out.

 

The honking is your vehicle alarm going off, which will happen immediately you reconnect a good 12 V supply back to the car. Just close up your car and lock it with the remote, then unlock it to reset the alarm.

Yes, you can. For the AGM battery that the Pruis uses, these voltages will give a rough indication of battery state. Bear in mind that the amperage that can be delivered is also important (but this is another discussion for another day).

12.9-13.1 V ..... Fully charged
12.7 V ............. 75% charge
12.1 V ............... 0% charge.

Anything above 12.7 is acceptable. Anything less, the battery requires charging. If the battery won't maintain 12.5 or better under the load of your headlights (on low beam is sufficient), then the battery condition is declining. Even so, your battery will continue to work for quite some time yet. It is not ready for replacing, I would say when the battery cannot sustain 11.5 V under the load of just your headlights running, then it time to start shopping for a new battery. (also note, the battery voltage should bounce back to close to the starting voltage after the load is released. If it doesn't get close, that is also a sign of a battery in poor health.)

Everything you have said indicates the 12V battery is past its "use by" date. Take the car back the dealership from which you purchased and insist that the battery is replaced. Do not accept the line that they usually spin - that they tested it and it checked out ok or we just need to give it a charge and it'll be ok. It is not ok. You already did that twice. Just tell them, "yeah well, in the real world it is not ok and will not reliably start the car and will not hold a charge.

Hope it goes well and you get a good outcome without too much of a fight.

hope this helps

 

yep. take it back to the place you bought it and politely demand a new battery. if polite don't work, then get angry.