Yeah E8 you are kinda up a creek. E8 is a Chinese wholesaler model, sort of a miniature of KR808D-1 w/ less voltage, and I don't know any vendors that use E8. This rebrander might still sell an E8 not their PR110):
http://www.premiumecigarette.com/
IMO - If you want slim ecigs, accept 9.2mm diameter and look at KR808D-1 at Vapor4Life.com (which is like the original manufacturer model) and a slightly different style at SmokelessImage, Bloogplanet, Halocigs G6
I recommend manual batteries if you will be refilling cartomizers (I can get a week of use out of each carto by keeping them damp with suitable liquid). Vapor4Life manuals are somewhat sealed inside and have an easy to press button. The others I listed may be rubberized (Volt is) and claim slightly longer charge w/ fully sealed threaded end on the manuals but a tiny partially recessed harder to press button and possibly a shorter safety cut-off (may restrict to a slightly shorter drag vs the Vapor4Life). Manuals make it easier to get a good hit and are harder to damage or kill with juice leaks. Sizes 180/220mah, and for the standard aka 78mm 280/320mah for 120mm length assembled (the Volt/Bloog/Halo type claims the longer battery charge but is very slightly less voltage with 3.6 vs 3.7v)
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Alternately - Joye 510 manual 180mah, Joye 510 mega xl manual 280mah (and 128mm long with a cartomizer). Joye Ego 650mah+. Or the Riva 510 650mah from Liberty-Flights.com (the kits there are 3.7v so a bit higher voltage than Ego and the new SE model has a 3-click on/off feature). The fat battery models have the option of using the hotter low resistance atomizers and cartomizers.
100mah is about 1 hour of moderate vaping
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To get a week use out of each I use thin liquids, PG with 20% or less VG (often 10% or less), and I avoid liquids that seem to drop a lot of carto-clogging flavoring sediment