(oops sorry about 2 posts in a row)
If you think he would want a slim ecig - nothing slimmer than what you have is any good.
I don't know which 808D you have (the oddball KR808D-2 which just a few rebranders use or the well-supported KR808D-1 which sold under its own model number and by rebranders and is also supported by 3rd party cartomizer makers). But both are 3.7v slim minis - strongest slim mini you can get and decent battery life with standard aka 78mm size batteries.
I recommend manual batteries - easier to get a good hit and harder to damage or kill with juice leaks. AT least try a manual battery.
Look at SmokelessImage, Bloogplanet, Halocigs G6. These are all rubberized and have a bit more charge and a better sealed threaded end on the manuals.
The other choice - Vapor4Life - not rubberized and allows longer drags (cutoff at 10-13 seconds vs 5 seconds for the other KR808D-1's) so even with manuals where you can press the button 1-2 seconds early to have vapor waiting when you start to drag, there is plenty of time left to drag with the Vapor4Life ones.
He seems to like your model fine so consider getting one of the above for him. And if yours in not thread compatible, you can get D1 <> D2 adapters if you want at leCig.com (I don't recommend their cartos though - not slotted acorss the center post, bad air flow)