I would just put the card in your PC and format it. If it formats without error, then you're probably okay.
Depending on the version of Windows (or Mac OS) you might have the ability to scan it using the disk drive utilities built into the OS. The only other thing to do is make sure that the capacity of the card roughly matches what Windows/Mac says is available after formatting. There are invisible files on the card that take up space, so the capacity/available numbers will never match up perfectly. Comparing to a new or known good card might also help determine the overall health of the card.
GoPro battery life can depend on the age of the battery, the number of discharge/charge cycles it has, state of charge at the beginning and ambient temperature. I always start with a full charge, which I top off right before a ride. I also turn off anything I don't need - bluetooth, voice commands, etc. Keep it simple, in terms of what the camera is going to be doing for the next 2 hours. I have a Hero 7 and can usually get 2 hours on a charge if ambient temp is -6C (just a guess) or warmer (20F). Once the temp is closer to -16C (0F), then a charge might last an hour and a half at most (sometimes less).
On my last ride, I carried a battery pack cell phone charger and about half way through the ride I plugged the camera in and stuck it inside my coat to let body heat warm it up. That worked pretty well and for the first time ran out of memory before I ran out of battery. Most of the time, I just let it run until it dies.