Cox glow heads are in general very sturdy and you can crank up the volts/amps until they light up like a flashlight. The major problem people have in starting Cox engines is not having the glow plug hot enough. I use a two volt 5 amp/hr gell cell. In the mouseracing days it was mounted on the left wrist with two short leads going to a hot thumb. I have plugs that have 100's of flights on them, and a couple which died before I got the engine started the first time. So there is some variability, but most are sturdy.