Given the age of the devices, and that this is a retro-activity anyway, I would suggest one of the Palm III or Palm m1xx devices -- most of them take AAA batter

Given the age of the devices, and that this is a retro-activity anyway, I would suggest one of the Palm III or Palm m1xx devices -- most of them take AAA batteries, not a built-in rechargeable. And will give you the experience of the typical heyday of Palm OS. (By the time large colour screens rechargeable batteries and WiFi became standard, Palm was already already well into decline.)