100w!? That's what I use in my campervan to the fridge, outlets and lights. A bit overkill for the old Prius. Out of interest though, how have you mounted it and did it reduce mpg?
That was on my old car haha, I will be gluing 2x 110w flexible panels on the Prius but I havnt finished it yet, I don't forsee them affecting mileage a measurable amount, I've removed the antenna and rear windscreen wiper to compensate for the small aerodynamic loss. Obviously I'm doing much more than just keeping the 12v battery charged while it's parked, I often run power tools for work and music and lighting equipment at parties and camping stuff on weekends.
I've read that when mounting those flexible panels directly on a roof, they don't last very long because they over heat.
Yeah that's why I havnt done it yet, I need to find some thin plastic strips or something similar to lift it slightly above the roof to let the heat escape
The adhesive I'm using is incredibly strong, but il see how it feels once they are on, I may put bolts through as well for extra security
Maybe use some sort of a weather seal to create a sort of spoiler in front of the panel, like on a yakima or thule roof rack, but much, much smaller. I know the adhesives nowadays are super strong, but just another bit of protection for peace of mind.
As an update, I had the 12v on a trickle charger while I reconditioned the hybrid battery. Even after a few days, the voltage only reads 12.4v. So it's definitely buggered. I'll be looking for a cheaper than OEM replacement shortly.
OR your "trickle charger" doesn't have the capacity to bring it back from near death. But the odds are indeed with the battery being bad.