Even though the warranty has expired, you began chasing this problem before that point. It seems to me that you should still be able to get a warranty replacement. I would get very forceful about it and demand a replacement camera. You spent good money on the rig and this is clearly not an acceptable situation. Any camera shop that sells underwater cameras should understand that ejecting the battery to reboot the camera is NOT an acceptable solution below sea level. They need to make good on this deal.

As for battery storage, the best bet is to fully charge it after use, then eject it and keep it with the camera. The DC600 comes with a leather carry case that has a seperate little pocket just for the battery. They do discharge over time, so if it sits for a while be sure to top off the charge before you giant stride.

Mountain Dog