there's no need to stick the guts of it in the window, you can hide it away so it can be kept cooler than the majority of other battery powered models, if the battery gets punctured there's a fire risk, if it's just heat affected they generally swell up long before that happens, it does use a standard GoPro battery so you can buy decent quality replacements if you're concerned that the included battery was low grade and more of a risk, the fact that you can hide it away and keep it away from the heat negates a lot of the risk
that said I wouldn't consider powering it permanently while parked, that can increase the risks of battery failure due to the added temps