When you change your battery, change your memory card. This way if you have an accident, you will only lose the data on the card in the machine. Everything previous will be safe.
Do you want to shoot in 4K or 1080p constantly?
If you answered yes then you need to make sure you have a fast card.
Having maximum storage (64GB) is one thing but allowing the data to be saved at the rate that it is recording is your limiting factor.
The SanDisk Extreme series of cards provides Speed Class 3, compatible Class 10 which gives write speed of 40 MB/s so you dont miss a thing.
Speed Class 3 compatibility allows you to shoot photos in continuous burst mode, and record Full HD, and 4K Ultra HD video. Includes SD adapter for compatibility with full size SD, SDHC, and SDXC devices.
Added features include: Shockproof, Temperature Extremes, Waterproof, X-Ray Proof and operating temperature of -25 to 85C