12 v Battery Drain

1. You used one of those random number generator battery tester; those numbers are derived from a 3-5W load resistor within the unit.
2. It showed you 10Ah and you seem to know what an OEM battery should be, so how did you reconcile that one and how did it fool you????
3. You didn't use a carbon-pile load tester - Even the cheapest carbon-pile load tester would've failed that battery. No calculations needed.

enough said; I'm done.....

 

loose connection or bad ground point somewhere??? Obviously not in the traction pack, since it worked in the other car. I'd be looking at the motor/transmission ground cables.

 

The testers were both the type that use frequency tests on the battery to estimate its properties. They don't actually load the battery at all as part of the test, other than by drawing some current to power themselves. That is the method used by pretty much any small electronic tester these days, including the Midtronics one encounters at the Toyota dealership. Conveniently, for the dealers, these testers cannot fail a battery for lack of capacity.

The 10Ah capacity was derived from checking the voltage after extended discharge and unloaded recovery, not from the electronic testers. As I said, the few electronic battery testers that claim to provide an Ah reading are just making it up. For instance:

Battery University | Perception of a Battery Tester

begins with

Various sources put the fraction of lead acid battery failures from "capacity fade" at just under 50%.

A carbon pile load tester will fail a battery if its internal resistance has gone up high enough. In the battery which was replaced it was not yet very high. The Prius and many other EVs and hybrids that do not use a starter motor only pull a few tens of amps to start the car. That is the appropriate sort of load to apply when testing them. They aren't designed to put out 200A, some of these batteries might fail permanently if they were presented with a load that large. These are essentially storage batteries (toughened up to survive the environment in a car), not starter batteries, and the large current test methods appropriate for the latter are not right for the former.

 

That was just an example for the current state of that battery. Another way to think about this is, if the battery new had N Ah, and 4 years later you measure N/4 Ah, then the writing is on the wall that it will be even lower than that some time later. Ideally one could attach a device, press a button, and conveniently measure the capacity. As things stand now, measuring the capacity takes a long time and is not at all convenient. Eventually it will get down to the point where the car won't start - quite possibly without failing a test on an electronic tester even at the end. (Or it could develop an actual fault, then it would fail, but capacity fade isn't that kind of fault.)