Using a DeWALT 18v or 20v battery you can use this adapter to charge your mug for hours. The charger has a built in voltmeter to keep track of the batteries charge.
You can use genuine or compatible batteries and the higher the AH then the longer it will power the mug.
I tend to make these chargers with any spare filament that I have, so colour is not guaranteed but if you require a specific colour please make your purchase on cymruchargers.com and drop me a message alone with the purchase. You can add on an illuminated charger, desk charger or mini-charger at a reduced price if needed.
I've run multiple test with different sized batteries and a 5ah battery will power the mug for about 6 hours, a 4ah battery runs about 4.5-5 hours and a 2ah battery about 2.5 hours. Depending on the age of your battery, these results may vary.
 
Please note: The battery and DeWALT chargers are not supplied and you will need to purchase these yourself.
When the battery reaches about 17v the battery icon on the mug will start to flash. At this point you can switch off the charger for a few minutes and maybe get a bit more charge but really you need to swap batteries or recharge the drained one..