I think the battery is ok.I took the device out,have it full charge and it's still full when I check it a day after.
But I no longer have it in my car anymore.
The problem should be software.If I turn of the engine either w/ or w/o FireEye on screen,battery will be empty in just a few hours or in the morning.
You can not rely on the date of the recorded video and I'm not sure when the memory is full.Which record It will erase since the time will go back to 20000101.
Sometime even I manually shut down the system.I still found dead battery in the morning too.
Build quality of the device is ok except the useless IR lights but the software is really suck.
Just focus on the time reset issue. If you turn it off and the time still resets, it's defective.