This is my first post on this forum and I would like to share my thoughts on this subject.
First of all I strongly believe that any GTD system, be it paper or electronic should stay as simple as possible, so you don't have to think over and over every time what to do in which case.
In my case, the standard GTD setup works just fine.
It also took me some time to figure out how to handle projects in a natural way, big or small should be handled in the same way in my opinion.
For my personal system, I use Outlook. Then I synchronyse to a Windows Mobile phone for out of the office use.
When I come up with a new project, I put it on my master project list (I have one business and one personal, because this works better for me).
In the notes fields I put all the actions related (this can be 2 or as much as 20 or 50 for large projects). Put only the one next action that can kick the project forward.
I strongly disadvise to put actions on to your NA lists that are still have other dependences. In the battery example just "check battery size" should be on your @home list. If you are in the shop and you find "Buy batteries" on your @errands list, without having checked the size, you will end up losing time in the shop. In the long run you will stop using your system because you loose faith in it.
These tips are all from personal experiences and beleive me I have given up on GTD over the past few years. The best tip for me still is to keep it as simple as works for you.