Took about 4 hours to charge. The pressure seems fairly accurate on my other gauges, and the temp seems to match the outside temp when parked in the garage overnight. Has worked for over a month with no initial charge and sat in a door pocket with no solar power. Put it on the dash and the solar panel will extend the run time I haven't had to recharge yet. The weather has also been cloudy, with only a few days of sunshine over the past few weeks. Works well. Update: It's been on the dash for a few months now and I haven't had to plug it in to charge yet. The little stickers on the valve stems didn't survive the weather, but that's okay. I have attached a scanned copy of the instructions.