Usually you charge your Pilot-24 Lite CPAP battery with the mains adapter of your own CPAP device. Especially with the ResMed AirMini it is recommended by the manufacturer to use the Medistrom AC Power Supply, because the AirMini power supply takes about 5 hours to charge the battery. The Medistrom AC Power Supply allows you to charge your CPAP battery considerably faster, in around 2.5 hours.