External battery for older Trail cams

[Rundie]

I have some older Moultrie (M880 gen 2) cams that still work fine, but are hard on AA batteries. I'm aware that Moultrie still peddles their battery box, but I have a small Lifepo 12V battery (24 Ah and about 5lbs in weight) that I'd like to use. The cams have a 12V port for an external battery. My concern is - will the Lifepo battery work ok with the cams and not fry the electronics ? Also, when an external battery is used, does the battery tray with it's 8 AA batteries need to be removed ?