if you smoke that much then for slim ecigs I only recommend the 280-320mah ones.
100mah is about 1 hour of moderate
vaping
Joye 510 mega xl w/ manual batteries - 280mah, use Boge cartomizers for your favorite thinner juices, This is 128mm long w/ a cartomizer. the PCC is metal and hold one battery (maybe 2 with one charging) and 2-3 other items. This is a 3-piece so there are few prefilled cartomizer other than stock Chinese ones but since 510 is the most popualr threading there are lots of blank cartomizers. With the manuals you can use a drip tip on the atomizer for testing juices. I know FreedomSMokeUSA has some Joye 510 mega xl manual kits.
KR808D-1 standard aka 78mm battery size (not the shorty size) which makes a 120mm ecig w/ a carto. The standard manufacturer model and Vapor4Life model are 280mah, the SmokelessImage Volt model claims 320mah. I recommend the Vapor4Life only because the button of the manual are more normal size. The button of the Volt manual is tiny and recessed and harder to press but the threaded end is more totally sealed. If you wear tight jeans and what to keep the ecig in yoru jeans, maybe you will press the tiny less easily pressed button. I use both. This is a 2-piece so there are lots of prefilled cartomizers (and plenty of blanks). To test juices on a manual battery use a DSE901 atomizer and drip tip.
I vape both. I would day the Joye 510 w/ a Boge carto is a warm moist vapory hit and easier to get a larger amount of vapor (easier airflow). The Vapor4Life is a hotter model (full 3.7v) and with the warmer cartos like Vapor4Life WOW cartos and the Smokeless Image cartos it can pack more throat hit with the same jucie vs the 510. The hit of the KR808D-1 is a hotter, dryer and less vapory hit.
Prefilled is just a small convenience and not even that if you don't like the juice. To be cost-efficient, juice will be added to all cartomizers.
I do not recommend auto batteries with refilled cartomizers. If a cartomizer leaks, it will leak right over where an auto battery can be damaged - right over the hole in the threaded end and behind that is the auto battery's necessary little drag switch. Gunk that up or short it and the battery is probably ruined. Manuals also make it easier to get a good hit.
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If you are willing to look at fat battery models to get more hours of charge and ability to use the hot LR (low reisstance) atomizers and cartomizers), go to Liberty-Flights.com, press the 20% off, and look at EGo and its popular clone Riva 510 (and the Riva 510s they have are also slightly higher voltage).