Parasitic battery drain

Hello! My Prius battery has been having some trouble over the past couple months. I'm going to try including all of the relevant context.

The primary issue: the battery is draining over night. Not necessarily over one, single night. It could be a few days of non-use, or a week. Though sometimes it is just one, single night. The result is the same: I try to turn the car on, to no avail, the battery is dead and needs to be jumped. So of course first thing I did was take it in to Pep Boys to have the battery evaluated. Voila! The battery was totally dead and needed to be replaced. Splendid. Problem solved! Until the same exact problem persisted with the new battery. I even returned to Pep Boys claiming the new battery they gave me might be no good, but they then ran the necessary tests on it showing me that it is in fact a perfectly good battery. They suggested that if the problem persists then it is most likely a parasitic drain. From there, I test for a parasitic draw using a multimeter which gives me a reading of approximately -2.0A. I then pull each fuse (in the fuse box under the hood) and find that there is one that, when pulled, drops the reading to -0.2A (seems like there still may be an additional drawing source but we'll have to worry about that another time). The fuse is that of ECU B, with a corresponding ampere of 7.5, and which is responsible for the "smart key system, personal lights, gauges and meters, emergency flashers"—as per the vehicle's manual.

A couple more *possible* considerations. For the months prior to this particular issue, I was getting messages from my Prius that the key fob battery was low. I responded by switching to the spare key fob, rather than replace the battery itself. Could that be affecting the "smart key system" and causing the parasitic drain? I was also just reading a different article that claims that in order to do a parasitic draw test with a multimeter, the car's battery should be fully charged, and all windows and doors should be shut. Well, in my case, the battery of my Prius was dead and the back hatch was open (since that's where the battery is located so how else are you supposed to access it??). Does this mean the parasitic draw test that I ran was meaningless?

I'd love for any and all help, for if I can't solve it on my own, it'd be great to have as much information as possible to relay to the mechanic. Thanks a bunch!

 

What does using the back hatch's manual release accomplish?

Will you please elaborate on the Smart Key system's affect? Are you saying that by having the key fob present, there will inherently be a parasitic draw occurring? Also, how do you "block off the switch that activates the door open signal"? I should add that the interior lights were indeed turned off while I ran the draw test.

No new accessories. Though I somehow left out of my first post that I did happen to have a rodent infestation that roughly coincided with the issues. So my deep dark fear is that that is the cause of this. Though I don't know if it'd explain the intermittence of the issue (?).

Back to the fist point, though, I did not run the test with a full battery I don't believe. Can I use the multimeter to do that?

 

I just saw a video explaining that you can do the draw test with the hatch/trunk closed and the multimeter on the outside of the vehicle. Shaves off around 1.5A, apparently. I'll re-do the test as soon as I can and report back.

 

Thanks for all the info! The thing with the fob, though, is that the car's been dying with or without the key fob in the vicinity. So, presumably, if that were the issue, it'd have to do with the car's proximity detector itself (searching for any and all key fobs nearby) rather than my key fob. The way to test this would be disabling the SKS from within the car, correct?

 

That is correct, but I'm talking about when the engine is off. The battery is draining while the car and engine are completely powered down.