It's happening to all the 2020 Hybrids, not sure about the 2019 models. There's something that's coming on, or never going off that will drain the puny Aux battery. It's probably a software fix that needs to be implemented. The charging is done by a DC-DC connection via the main hybrid drive cells (no altenator in a hybrid). I've checked my voltages while it's "running" and the charge voltage is fine (roughly 14.5v). I've started puting a battery tender on it once a week, but shouldn't have to go through BS like that. It's not like it's a Jaguar or Benz. I know it will still happen again if I let the car sit for a day or more. This is pathetic. Long time Toyota owner, maybe not for much longer after this. I have a case open with Toyota (twice), and have started the lemon-law paperwork. Toyota needs to fix this! All I can tell folks is to open a case with Toyota, and tell them you'll stop buying their brand if they don't remedy the problem.