Prius stuck in endlessly locking/unlocking door loop, drained battery, wouldn't start?

I got the car running again, so no need to go into details on that (I used the physical key on the keyfob, you really do have to turn it further than you'd think, but that got me into the car, after several tries was able to get it to stop cycling through the locking/unlocking and was able to jump it).

Got the 12v battery in my Prius replaced by the dealership in the last 2 years. Last winter, one day my Prius refused to start even though it had been running fine earlier that day and was parked in a semi-heated garage. Jumped it and got it working.

Last Friday I went to get out of my car and my Prius kept beeping at my any time I had the door open, and the clock on the dash seemed to be a little dim. I doubled checked that the keyfob was in my pocket (and not in the holder thingy), eventually the car seemed to lock fine and I went up to my apartment. Didn't drive the car until this morning.

This morning I come down to find that keyless entry does not work, nor does pressing the unlock button on the keyfob. (The car is parked in heated underground parking fyi.) About every 1 second on repeat, the car is making this sound like it makes when you hit the lock/unlock button from the inside of the car, so it seemed like it was stuck in an endless loop of locking or unlocking. I go back upstairs, leave my key fob in my apartment (which is around 300 meters away or so), come back down - it's still on the loop making that sound.

I get into the car with the physical door key, try starting it - the lights will come on but the car doesn't seem to actually start. And the endless lock/unlock loop starts up against once I turn the car "off". I got upstairs and switch to my other backup keyfob. Come back down. Car is still in the endless loop. Try to start it again, car still doesn't seem to start, but this time when I turn it "off" the endless lock/unlock cycle finally stops. Do finally get it running by jumping the battery, then it seems to run fine.

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So I bring it to the dealer, and the guy their rather vehemently insist there must be something wrong with my keyfob. First he immediately confidently assures me that I just need to replace the battery in the keyfob, which makes no sense. Then he changes to saying he thinks the lock button on the keyfob was stuck down, which doesn't make sense either as like I said it continued doing it even when I removed any keyfob from being anywhere near the car. The dealership guy tells me - and yes I'm serious here - that the dealership won't work on any problem that they cannot reproduce at the dealership. He tells me if I want them to look at it there's a $150 diagnostics fee. I've seen a lot of bizarre dealership stuff, but this is the first time I've seen them actively trying to get me not to spend money on my actual problem at the dealership. So I had to leave.

Has anyone else had a similar problem or any suggestions? I live in Minnesota, and I'm freaking out a little that I'll come out to my car to find it needed a jump at -5 degrees some day this winter. (Which fyi I know from experience, if your battery doesn't have a charge it can freeze in the winter and you can't jump it until it's warmed up again.)

 

If it simply died the second time, I wouldn't even be posting, I'd just be assuming it was the battery. What I don't understand is the endless loop lock/or unlock cycle it got stuck in. A little worried there's something else wrong, like a malfunctioning sensor. It's not the only "ghost in the machine" experience I've had with the vehicle. While nothing dangerous has happened, I've had weird things happen like if I turn off the car then open the door in a certain combination the car comes back on on it's own. The first 3 times it happened I thought it was my fault, but after several more times I was 100% sure I wasn't hitting the power switch again.

The bizarre thing about the previous time I had to jump it was that I had replaced the battery not to long ago, I had driven the car earlier that day, there was nothing obviously high drain on for the car (headlights seemed to be off, and interior lights wouldn't have drained the battery in the 4-8 hours between when I had last driven it), and it was inside a tuck-under garage so it wasn't even outside in the cold - probably 50 degrees in there.

I'll go the the dealership...uh, another dealership tonight, and have them test the battery and see if it's good. If it's not maybe I can get it replaced under warranty. Will try switching around which keyfob I'm using as well...and keeping my cell phone charged.

 

It still makes the "constant locking/unlocking" thing bizarre and unexplained though. And the battery was inside in a well heated underground garage.

 

Interesting info. I'm going to have the battery tested and if it's bad see if I can get it replaced under warranty, but if that doesn't work out maybe I'll replace it anyways. Something weird is going on.

It looks like it's $150 on amazon -

Even if I don't want to replace it myself, I can probably buy it and get a local shop to do it for a minimal charge. The dealership did a crappy job last time anyways, don't see an advantage in using them again.

I have done all the work already in order to be able to get at the battery and jump it, so replacing it myself might not be to hard. I have an indoor well heated garage to do it in as well. I just vaguely remember reading something about special steps being needed with a Prius battery above just unscrewing the terminals from the old one and screwing them back on on the new one.

 

The second theory was that there was something jammed up inside the keyfob. I already replaced the keyfob batteries a year or two ago, and they still worked fine otherwise, so the "jammed up keyfob" or "defective 12 volt battery" seem like the most likely cuplrits other than "bizarre electronics problem".

 

Yeah, thanks for the mention, but there's a few drawbacks of that:
1. The one under the hood had a "protective" plastic pieces around it that make it difficult to attach a big battery jump clamp to
2. To get under the hook you have to be able to get into the car first anyways, to hit the lever that unlatches the hood
3. I was parked in an underground parking space with the front of the car facing the wall, it was actually much easier to get into the trunk to hook up the battery jumper than it was to try to get at the one under the hood
4. The under the hood location also doesn't have an easy flat surface to place the battery jumper on. I've done it before, it can work, but going directly for the battery in the trunk is actually easier.

Thanks for the mention of it though.