Well I did a test and determined that the plug was lit for approximately 45 minutes and tapered off quickly thereafter. When I charged the battery I could only get it to 1.39 volts - I was expecting around 1.5. So I am not sure if the battery is really getting its max capacity. If my assumption is right, theoretically I should be able to get around 2 hours of glow with the 4000 Mah battery (2 2000 Mah in parallel) if the plug draws around 2 Amps.