I had an old galaxy a5 with a badly degraded battery sitting around. A few weeks ago I had nothing better to do so I opened it (breaking the glass back in the process because of how strongly it was glued), ripped the battery out and soldered a charging cable straight to the phone's battery contacts. It now lives on a phone stand in my car, connected to a bluetooth OBD2 scanner and I use it to show a couple of additional gauges like oil temperature, instant fuel economy and engine load while driving. The 12v output provides just enough power for the phone to reliably run and with the lack of battery I don't have to worry about it exploding if it sits in the sun for hours. I haven't found a way to make it turn on as soon as it gets power, so it's mildly annoying to turn it on manually every time I start the car, but I can live with that.