Prius 12V Battery went dead in 20 hours, Fob key won't unlock door

but how do we know it's bad? maybe the amp is drawing it down faster than it can recharge?

 

You can disconnect negative battery lead, push a chain link ( or similar) into the hatch latch to simulate hatch closed, wait maybe 20 minutes then connect miniameter. I measured 16~20, with occasional spikes to around 45, which I think is normal case.

 

The best way to prove a bad battery is to replace it. I have had a lot of bad batterys over the years. In most cases it is easier to buy a new battery than to play games with the dealers

 

No offense, but I'd say that's the WORST way to test a battery. How about acquire a tester like Solar BA5? Then you're not flying blind.

 

I'd be still going with disconnecting the non-original stuff, returning it to stock first. If that solves the problem, then work out which of them is incompatible. If not, maybe the battery is indeed dead.

 

What's the point paying out for a new battery if the fault lies elsewhere ?

 

If it is bad, it may be replaced under Toyota's warranty. I remember at least one other battery replaced extremely early under warranty here.

 

Perhaps this is a cautionary tale to warn modders about interfering with the default Toyota Prius electrics...
.. unless they're absolutely certain they know what they're doing.

 

If the wife gets stuck a couple times in her brand new sienna, it is real easy to replace the battery.

 

How does that apply here?
The Sienna is not a hybrid and the battery has the engine starting stresses that the Prius one does not.

 

Bad batteries are bad batteries. Has he Found a fix yet.

 

There's no denying that, but to suggest that a flat battery is a bad battery and to change it would cure the problem, doesn't make sense.