I have 2 different glow drivers. One's a Tower hobbies 1600mAh NiCD, and the other is a Dynamite sub-c with gauge and a Batteries plus 2100mAh sub-c cell in it. 1 good charge on either driver and I can go run for 2 or 3 days on a single charge. (I always carry two drivers should one croak mid-day)

The + post of the battery should always go to the center post on the glow plug, and at least on my Dynamite driver that would have the + post facing towards the glow plug.

The higher the mAh rating, the longer the charge will last provided its charged slowly. NiCD's will take a charge memory - if you dont fully discharge and recharge it, it will take a memory to that pattern and you will end up with decreased battery life. NiMH batteries have a lower tendency to do this but are a little more expensive.. I charge mine at 170mAh.

Either of my drivers will make a glow plug glow orange. New plug or Old, doesnt matter. Hotter plugs will be brighter orange than colder plugs because of the coil's wire diameter.

+1 for rechargeable drivers.