I wouldnt use 2.0ohm cartos on a slim ecig battery. It might work okay for awhile, but the constant stress on the battery will def kill it faster.
You also have to remember that a carto isnt always exactly the ohms that its stated to be. Normally their +/- .2ohm. Also, most cartos generally drop slightly in ohms after youve been using it for awhile. So if a 2.0ohm carto is actually running at around 1.8ohms, your prob going to fry a slim ecig. A 2.0ohm carto already puts a lot of stress on a slim ecig, and if it drops lower, you really risk frying the battery. Thats why I recommend using 3.0ohm cartos for a slim ecig. Then at least if it drops slightly, youll still be okay.
I wouldnt use LR cartos on a slim ecig, but if you are going to continue using them, I would at least use a multimeter and check EVERY one before you use it to make sure their at least the stated 2.0ohms. Also I would check them again every few days to make sure they havent dropped in ohms bc of use. If its any lower, do NOT keep using it. Youll be less likely to fry the battery that way.
If you dont have a multimeter you can get the one that madvapes sells on ebay for $3-4 bucks, and they give free shipping. It does come from China so it takes alittle longer to get to you, but it does work well and serves its purpose. Type in DT-830B multimeter in the ebay search and it will bring up a bunch of them for sale from different sellers. Look thru them and find the cheapest one. Madvapes sells it for $10+shipping. On ebay its alot cheaper. I found ones for about $3.50 but it doesnt come with a 9V battery. I dont have any 9V batteries at my house so I ordered the one for about $4.50 that comes with a 9V battery already in it. If you have a 9V already tho, then you can get one for under $4 bucks. Its def worth it