Dead Battery?

I am stuck and will probably go deal with it before I get an answer here, BUT.....

Came out to start my 2013 Prius level3, and the electronics came up, acting very funny, lots of indicator lights flashing and acting very different than normal but the car won't start. Actually it did for a few seconds run and I was able to back it half way out of the garage but then stopped. Now I am stuck because of course you can't push a dead prius. Hoping the wife doesn't accidentally try to close the garage door.

I've got about 70K on the car and have never changed the 12V battery. I am hoping that a dead battery is the case. They cost $200, plus return charge and tax so i will be into it for $250 to find out if I simply need a new battery or whether something else is wrong.

I pulled the battery (after climbing around to get access to the latch for the rear hatch door) and I've put a very old generation simple charger on the battery and it is pegged to maximum current trying to charge. Not sure if that means anything.

UPDATE: in the last hour the meter on the charger has gone from pinned at 8 amps down to about 5 amps. - I haven't used this old charger on the Prius before, but on other cars when I've used it to recharge a battery that was dead from leaving a door open, the battery charger never goes down below 4amps even when the battery has been recharged. So I am not expecting it to drop to 0 as I fully charge the Prius battery. I am not sure what length of time it would take on the Prius battery and what level it will show.

I unplugged the charger, put it back in the car and was able to get the car to come on and move it a few feet back to inside the garage and then it died again. I am wondering if leaving on the charger longer will bring it back to life and whether I can avoid buying a new battery, or if this is just further evidence that I simply need a new battery.

 

Bought a new battery and replaced it. Problem solved. The battery was the original 2013 battery so at least 7 years 4 month old, even though i don't have a lot of mileage on the car. I think I did not leave any lights on or doors open. I think it just died on its own.

Car is running again. While working on the car, I was cursing the design of the car..... can't roll it with a dead battery, and can't unlatch the tail door from the outside. You have to get inside on your stomach and fish around to find the little latch in an awkward place.

But the car is fixed and like my Prius again.