The mobile printer that we support are manufactured by Gprinter. We use the model PT-280. Here is a link to get them direct from manufacturer. The manufacturer also makes soft carry cases for the printers with belt straps. They generally come in a case of 10. It takes 2 weeks for them to manufacturer them, and generally another week to ship them.
We see the printer work for 2000 to 3000 prints a day without battery issue. To charge the printer, you have to plug it it in and turn the printer on. The reason for this is to prevent the printers from getting over charged.
The printers we use all take standard Thermal Paper. It needs to be 2.25" x 85' or 57mm x 26m rolls. You can by this from Office Depot locally or buy it online from Amazon. Clicking the image above takes you to Amazon where you can buy some.