have you tried connecting them via PC and opening Garmin express? The software maybe corrupted and reloading it is worth a try. Also, try swapping memory cards over. If the card gets corrupted or damaged from a 'hot pull' or power loss mid write it has a similar effect. Camera fails to boot up. I have one dodgy battery, that causes the camera to start, run for a second, reboot, try again then turn off. Yet it reads like a normal battery when charging it.