Kwanwa Cordless Digital LED Alarm Clock,2 Batteries Keep The Big 0.9'' Red LED Time Display Up to 2 Years Without Any External Power,Battery Powered Only 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 and operated only, 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. Great idea for trailer caravan,motor home,cruise boat tent cabin hunting lodge,RV Camping- fishing . The clock specifies their accuracy as +/- 45 seconds per month or 20 ppm(parts per million)