Kwanwa Cordless LED Alarm Clock Battery Powered Only,Great for Home,Trailer Caravan,Motor Home,Cruise Boat Tent Cabin Hunting Lodge Use 2 D size carbon batteries can keep time display about 1 year or use 2 D size Alkaline batteries can keep time display 18-24 months . Average operating currents is about 1MA ,W/o USB cable or power wire. 3V DC power battery powered battery operated only LED alarm clock, 4 Digit,auto dim .creative portable LED electronic alarm clock. Big 0.9"red time ,12 and 24 hour military time display ,one very loud daily alarm can be set. Display will become dim automatically during AM 12:00--AM 6:00.DC powered,Suitable for desk end table top shelf, and bedroom.bedside,kitchen.living room The clock specifies their accuracy as +/- 45 seconds per month or 20 ppm(parts per million)