We have managed to lose the rechargeable battery

All I have *left* is the battery from a unit that was stolen. Model number is BATT-2P. It's a 7.4 V 3600mAh Li-ion battery that clips onto the unit and has an external connecting power cord.

Oh my, not good. Well, you do need a battery pack. Contact the MFR for replacement pack via customer support, or check the voltage on the side, if using 9V, get a battery holder that uses 8 batteries[2 Xtra cells are used to disable the shutting off at too high a voltage due to the missing battery pack]go to battery space.com, and go to wires/connectors, and get the laptop connectors to make an external battery pack. Therte is a battery pack charger/I recommend accupower evolution. You have to google and go to other sites to get the rechargeable batteries and battery holder. You can get by with alkaline, but they would go rather fast due to the large screen size. You need that good brand name so they can be evenly charged due to the batteries being able to be run down further. You wont be wasting much voltage with alkaline due to the lower cutoff voltage, but 1st try contacting the mfr or googling to get that battery pack!!!I Hint: if using battery pack and you still want to add more battery life, drop the batteries to 6 on a 9V circuit. with original battery pack on, a 9V circuit would use 6 D cells on an external pack, 8 for a 12 volt.