Before you go down this route, is there a reason you can't just have your car in Ready mode? That way you'll be pulling power from the HV battery (and engine when necessary) instead. The reason I'm saying this is that the car shuts off the accessory mode electrics after 20 minutes anyway, unless the car is in Ready mode. I'm speaking as a parent that has to sit in the car outside of various venues for hours at a time while my kid(s) do dance, karate, etc. Ready Mode not only keeps your 12V battery going, but it doesn't turn off, and you have climate control.
There is no defined or packaged upgrade for this. You can obviously switch to a larger battery, or to multiple batteries, but you'd have to build it yourself or pay somebody to work it out for you. It wouldn't be difficult for someone who has done custom auto electric work. I think @The Professor's suggestion should help, unless there's a reason you can't leave the car in 'ready.'
sure, put the highest capacity battery in there that you can fit. idk if the charging system will keep up with it, but it is worth a shot
It isn't just about the battery. It is more about the capacity of the charging system......which in a hybrid is a voltage converter that is run off of the hybrid battery. If you are exceeding the capacity of that, you are screwed. BUT.....before you panic, you need to have your 12 V battery tested.....and the charging voltage. It is possible that your battery is just going bad. Note: And supplying some details about exactly what is happening might get you some better answers.
Following on from what Sam said, I'm in a 2017 Prius too, and while I'm blaming it on the reduced use of my car during this pandemic, my 12V battery went flat (to the point the car wouldn't go into Ready Mode) the other day, after just being in Accessory mode for about 10 minutes. The battery is probably getting old. I find most 12V batteries I've owned start to show fatigue after about 3 or 4 years.
