I've had one for 3 years now and always take the batteries out when not in use as for some reason it uses power when turned off. Its been very reliable and proved to be waterproof. The Go pro has about 3 mins of memory without a camera card so it may not be reading your card, you should have 2 or 3 files when you download if you use all the memory and you can change the quality to get up to 4 hours recording.
regards Jeff