1 gps is never enough. Always take 2. Don't ask me how I know! (btw, I had 2)

Keeping spare batteries sealed in a ziplock bag, that is sealed in another ziplock bag, that is sealed in a drybag, is not enough protection. Don't ask me how I know.

Removing batteries from the flashlight/strobe will get your GPS working again, but you'll have a damn hard time doing it in the dark (no flashlight). Don't ask me how I know.