I have an F4s on the way. Are modern rechargeable batteries (NiMH) safe to use with this camera? I believe the owner's manual specifies regular AA or Ni-Cd AA. I imagine some may have tried modern rechargeables in the F4s. If so, I am interested to know if there have been any issues. I gather cold weather performance is better with the NiMHs? If you have had success with a particular brand or type, please let me know. Thanks.