2004 Prius -- battery draining

1a) It could be they installed a 12V battery that was NOT fully charged.
1b) It could be they installed a wrong 12V battery that was NOT fully charged.

2) What battery group size was installed? Or provide the battery manufacture and part number.

3a) Positive and Negative terminal posts are tightened correctly?
3b) Negative battery cable BOLT going to the body is sufficiently tight and NOT LOOSE?

4a) Perform this load test on the 12V battery w/ a DVM (Digital Volt Meter).

1) Let car sit overnight.
2) Foot off break, press Start twice: IG-ON mode.
3) Headlights on HIGH
4) Vent fan on high, AC off
5) Radio on, low volume.
What reading do you get? Measure at the 12V battery terminal posts or the jumper posts in the engine compartment.

Another person has a different approach to load testing the Prius 12V AGM battery; I prefer my way b/c of a greater load:
1) With car off measure battery voltage at the front jump point. Write that down.
2) Then with car off, turn on headlights in high beam and leave them on for 5 minutes.
With headlights on at the end of 5 minutes measure the voltage.
3)Then turn headlights off and with car still off measure battery voltage. What are the 3 readings?​

4b) SOC (State of Charge) chart

5) Conspiracy theory. Sales department is pressuring service department to steer customers their way. Convenient excuse of we don't know how to fix a USA model Prius.

 

also could be that a short is causing higher drain then normal when off, which might have killed the original battery.

 

Two common causes of the 12v battery draining overnight are the capacitor backup for the brake system and the driver door courtesy lamp. The capacitor backup is located directly to the left of the 12v battery. It's a black box bolted to the trunk floor. It's been known to have a capacitor go bad and cause excessive drain on the battery. The courtesy light on the driver door works through the small button switch located in the driver door jam near the locking linkage.

It shouldn't be rocket science for a tech to determine parasitic battery drains.

 

Well, there is some truth to that:

1. NA Prius has additional emissions control equipment such as the engine coolant heat recovery system and the bladder-equipped fuel tank.
2. NA Prius has drum rear brakes while the European Prius probably has disk rear brakes.
3. I imagine that the headlights are different.

However I'm not aware that there are any significant electrical differences. In any event, the usual way to determine the root cause of the problem you described is to use a digital multimeter set to measure electrical current, and attach it inline with a battery cable, to measure the quiescent current draw. When the car is IG-OFF and doors/hatch locked, the quiescent current draw should be around 0.02A.

If the current draw is much higher, then you would have to start removing and replacing relays to see if you can determine the circuit which is causing the excess current draw. It could be that a relay is stuck closed. Sometimes if you tap the suspect relay (with a small screwdriver handle for example) that will cause it to release.