2024 Prime being left for 2 months

I wouldn't have a problem leaving my Prius hybrid battery plugged in for months at a time, but the 12V battery should have a maintainer on it. The last few battery chargers I've bought, have a "maintainer mode" built in.

I know this because my Gen 3 Prius Plug-in sat in a showroom for several months, but when I got it, the 12V battery was bad, and had to be replaced. It got that way because the dealer staff thought that leaving the hybrid battery plugged in would keep up the 12V battery. It does not. I presume they ran the 12V battery dead many times over the months, thus ruining it.

Based on my experience with my Gen 5, the 12V battery needs to be maintained, as it goes dead fairly quickly; varying from a few days to a few hours.

 

That is roughly 48% actual SOC (considering the upper and lower buffers and HEV reserve), which is within the 40–50% optimal range.

These are the formulas for the actual SOC:

Gen 4 Prius PHEV: Actual SOC = Gauge SOC × 0.635 + 25.5%
Gen 5 Prius PHEV: Actual SOC = Gauge SOC × 0.69 + 20%

I left my Gen 4 Prius PHEV at 25% gauge SOC when I went on vacation, which is roughly 41% actual SOC, right around the optimal range.

0% gauge SOC is somewhat below the optimal storage actual SOC. There could also be some self-discharge. So, it is better to leave them around 30% gauge SOC.

 

I know disconnecting the battery is a possible solution,
But I really hate resetting everything afterwards.