bwlacy, the batteries that stealth cam sells are sealed lead acid batteries which are different than regular car batteries, im not sure if it would be safe to use a deep cycle or something like that. However, you can buy a bigger SLA battery, for example if the one stealth cam sells is a 12v 5.0 AH, you can buy a 12v 12.0 AH and you will be getting more than twice the run time. You have to make sure that the voltage is correct whether its 6 or 12 but the AH rating, the higher the better. You can buy a 12.0 AH battery for $28 plus shipping from batterymart.com. An 18.0 AH is $35. The charger would be another $18. You should be able to buy the correct plug from radio shack, then buy some wire and you can make your own complete setup with twice the power. Ill have to look at my stealthcam external to see what it uses but I think it is either a 5.0 or 7.0AH.