Battery dies when door left open while parked

Welcome.

Why are you stumped the 12 volt battery is done? How many times have you had to jump start the car? if you say once that should have been a pretty good wake up for you.

Btw...the dead 12 volt battery is the most posted about thing on this site since this site began 110 years ago. I have no idea what will fit a G1 Prius but most people on this site will go with the oem battery or a yellow top for there G2.

 

There is no need to be stumped. The most likely cause is that the 12V battery was in marginal condition and just barely able to power up the electronics when you want to make the Prius READY. By leaving the door open, that put a 2A load on the battery and after 20 minutes, the drain was sufficient to deplete the battery.

If you install a new 12V battery and keep it fully-charged, it will withstand a moderate drain for a moderate time period.

You cannot use the same 12V battery for Classic as will fit the newer Prius because the Classic battery is on the left side of the trunk, hence the battery terminal polarity is reversed.

Check to see what kind of battery is currently installed. The original equipment battery had insufficient capacity and Toyota spec'd a Panasonic battery of larger physical size and capacity as replacement. The Panasonic battery had SAE terminals (vs. Japanese industry standard terminals on the OE battery which are of a smaller diameter.)

 

Take the battery to a autozone or similar and have them do a load test. Their test will ascertain the health of your battery. I don't know anything about the type of battery that goes into the Gen 1, but to be safe Ed's advice about oem is the easiest path.

 

The problem with load testing, at chain auto parts stores, is the 50A, 60A, 100A, or 150A load put on 12V batteries, is intended to test for batteries that CRANK a traditional engine with a starter. A Prius does not crank anything, thus the Prius AGM 12V battery has a very low CCA rating when compared to traditional 12V starter batteries. This is why load testing at auto parts stores produces many false positives.

Many threads here on how to load test the Prius by putting the car Ig-ON, turning headlights on, turning radio on, turning fan on high, etc. The more electronics, the greater the load. With such a load, the battery should read 12V. If below 12V, consider chaning or carry a jump pack in the car.

12V batteries don't last forever. how old is the current 12V battery? If 4-7yrs, seriously consider changing, or definetly carry a portable jump pack.