My 2012 plug-in was in the garage with nothing turned on. Was completely dead. Measured battery voltage--3.5 volts! Had battery tested and charged--was ok. Tested the discharge current--was 1.5 amp, reducing to 1.0 amp. Toyota service didn't know why this draw. (My son said he might have left the key fob in the car but that doesn't seem to make a difference in discharge current.) Now seems stable--voltage 12.42 volts. Anyone else experienced this phenomenon and discovered its source? Thanks, Tonus
a lot of people have had high discharge rates when the car is off. not particular to the plug in prius. unfortunately, it is usually a long and difficult search with some good knowledge of electronics and testing to find the culprit. are you saying that it is no longer discharging above spec? how old is the battery?
I'd be sceptical of how "ok" that battery is. Did "they" tell you the Cold Cranking Amps measured? Who was this, and what did they assess it with? Who did this, and what was the method? That's a massive draw, normal is around 20 milliampers, with spikes to around 40~50, the latter maybe due to the blinking security icon. Second this:
If you are talking measured off state parasitic draws of 1.5 amp decreasing to 1.0 amp (1000 ma), those are only acceptable in the first minute or two as varies ecus shutdown. Usually you are talking to a Toyota Service Advisor, not a mechanic. Most service advisors have never been a mechanic. Generally they are taking shorthand information from a tech and attempting to translate it for you. Often simple and understandable facts are screwed up by the time you hear it from a service advisor. A light left on can discharge a 12v battery overnight. Often the map lights are not automatically shutoff if they were manually engaged. The same goes for headlights.
How old is your 12v battery? Nothing lasts forever under the moon. Every battery eventually goes to the realm of the dead. Check it with a battery tester.
If it's indeed discharging at 1 amp (after the first minute or two, agreed) then you can narrow down the offending circuit like this. You need 2 people. Car is turned off for this test, we are looking at what it does while parked. The first person's job is to look at an ammeter that you've set to 10 amp DC mode and connected between the negative terminal of the battery and its lead (you need to disconnect the lead to do this). The second person's job is to remove and replace fuses, one at a time, to shut down individual circuits. When you get to the bad circuit, you can look at a wiring diagram if it is not obvious what is draining the battery from the circuit description and behavior. You can tell you found the culprit because when you take out the fuse, all of a sudden, the current drain goes practically to zero. Using this simple technique, we diagnosed a stubborn current drain situation on an old Camry. The problem proved to be that the relay for the rear window defroster had stuck closed, running the defroster endlessly until the battery drained.
