I have no idea how long it will last. I will tell you this though, I once used my flashlight to plug some cables into a computer under my desk that had poor lighting on a Friday. I completely forgot about it over the weekend and walked into my office that Sunday and noticed my flashlight was still on. It still seemed as bright as ever. I still haven't changed the batteries in over a year since that incidenet.
First of all no question is stupid especially if it gets you out of a bind. Yes, the batteries are to be placed in the aft end (the screw cap opposite the bulb) of the unit if it is like a standard maglite. I shipped mine down to Haiti and did not open them up but I have had many others and they always opened up from that end and there is no reason to believe they go in the bulb end as there is a mechanism for the switch and the bulb socket on that side. The positive side with the nipple goes toward the bulb. If this is a new unit and never has had batteries this is unusual but as the other guy said it can be very, very tight when new. If it is a used unit that someone gave you and it has batteries in it the possibility exists that the batteries exploded from heat and the corrosive affects of the chemicals has jammed the threads of the end cap. This happened to me a couple of times here in south Florida in a hot work van over the summer. Try to coat the threads with something not to heavy (light grease or a nickel or copper based never seez compound come to mind) in the future. This will help.
Hi! Make sure the connections from the bulb to the rest of the flashlight are secure, then try turning on the light. If that doesn't work, then use another new bulb, in case the old one has blown. Also, make sure the batteries are inserted properly, with the positive charges pointing upward...Hope this helps, if this doesn't work, then return the flashlight & get a new one! Thanks!
Purchase either EverReady or Duracell alkaline batteries [D]. If you use these batteries and they ever leak, you can send the flashlight back to MagLite and they will repair or replace it for free. I recently had to replace my 12 year old 3 cell MagLite, because I used cheapo batteries, and of course, they leaked and ruined the flashlight. It was the only time I didn't use EverReady. :-(
This works and it comes complete with 4 ea. "D" cell rechargeable batteries and a charger too.