Don't get caugt with a dead battery! Why guess how much energy a battery has? Instantly Monitor the level on any 12-volt battery for adequate power. Other battery energy gauges have a range of 8-16 volts but Tempo's reads 11.8 - 12.7 bolts for a more accuate reading that reflects the "dead" and "full" range of a 12-volt battery. Temperature compensatesd for a more accurate reading. Energy level is indicated as a percent level remaining on the battery. Alerts you to overcharges. Perimeter lighting on face.