What is the normal ohms to buy? 1.8 or 1.5
Uh, for what topper? And what battery?
If a fixed voltage battery, or a mech, I'd suggest the 1.8. If you have a variable battery, either VV or VW, then the 1.5 would be ok, but the 1.8 or even in the 2.2 range, would give you greater ability to fine tune to your tastes.
Sorry I use a Protank Mini 2 on a VV ego battery, I think they only go as low as 1.8 ohms anyways,
I've never had a unit stop working completely. Usually I replace the coil when the flavor degrades to the point that I can no longer stand it.
Every time I have completely failed to get a hit from a unit it has been a battery issue.