This Metered NI-STARTER® has a 1.5" barrel and is supplied with an UL Approved 110V AC Charger. The Battery is a NiMH 3800ma cell. It locks onto the glow plug. Just push down, rotate, and it's locked for hands free operation.It has a durable, shock resistant, dual faced amp meter to show the condition of your glow plug. When attached to your glow plug the meter will indicate plug condition, good or failed. This aids in determining the cause of many starting problems. The meter does not indicate the NI-STARTER charge condition