Are they very long? And what color does he vape?
128mm long
If white - Joye 510 Mega xl manual and use with the tan or white Boge cartomizers from NiteLiteVapor.us (only place I have seen the tan and white Boge cartos sold). The cartomizer is a combined disposable cartridge with internal atomizer - I can get 10 days out of each using clear thin juices if I keep the cartomizer damp (run them dry and you singe them). That combo would be 128mm long with a cartomizer - quite long. And all decent slim ecigs are a bit thicker than a cigarette. If he smokes black shermans - check Cignot - they may have black mega xl Joye 510 w/ red led and most places do not list LED color (sort of assumed blue on black 510). Hard to find black
batteries w. red LED.
100mm long
It may be easier to find the short standard 510 manual in black w/ red LED - very short battery life 180mah (100 mah is about 1 hour of moderate
vaping) and about 100mm long w/ a cartomizer attached.
Note - Cignot puts their name on the batteries so you may want to look elsewhere. And use black Boge cartomizers on black manual 510. Slim ecigs can only use standard resistance cartomizers (2.5 to 3 ohm, not the hotter LR stuff below 2.5 ohm). And in Boges I recommend 80PG/20VG juices.
As you can see I only recommend manual (press button to activate battery). The 510 manuals are fully sealed metal on the threaded end so they are safe from being damaged or killed by
juice leaks. And manuals make it easy to get a good hit.