I finally bit the bullet and spent some money on a 27000 mAh powerbank with pass-though charging up to 40W and a 17W 18V solar panel so this can be placed without needing mains power or someone to change the battery.

The vending machine and camera together draw about 1W when idle and about 4W when dispensing a peanut. I estimate about 1.5W on average. I should be able to keep this charged via solar - it can run for about 2 days on the powerbank alone so it can tolerate a couple dark days and stay running.

I should be receiving the goods this week to start testing this out. I would like this to be someting you can place anywhere and only have to refil the hopper occasionally. For now it will still need a wifi access point in range for remote access.

It works great. The 17W 18V solar panel charges the powerbank significantly faster than the vending machine and camera drain it.