Your LED bulb will let the battery last maybe six times a long as the old incandesent bulb. Actually if you calculate its current draw, 4 W at 12V is only 1/3 A. (1/3 A *12V=4W) So if you can really get 3.3 AH from the battery, it would last 9.9 hours. Probably it won't really last that long. You might get 5 hours though.
Mike W.
(published on 08/01/2016)
