Must be honest I'm a bit baffled by your comment in the OP about having to "keep recharging expensive rechargeable batteries"

How fast are they going through them ??

I've got half a dozen trail cameras of various makes and I have to change/download the SD cards well before the batteries show any sign of power drop,
If using the full bank of 8 batteries I'd be extremely disappointed if they lasted less than 6 months out in any of my cameras.