Yea I hope to get up to mods and such.... just looked at the Nemesis and ZMax, ugh... I just can't decide. :/
It's easy:
An eGo type battery like what you have is just a battery with some eletronics glued and soldered onto it.
Maybe the electronics will fail, but in any case eventually the battery itself will fail; it's only good for 100 to 300 recharges.
And before it goes it will deteriorate; it ain't going to sudden death, it's going to get old and slow and feeble.
A zmax uses replaceable standard sized 18650 batteries, so if you batteries start going weak, you put in new ones; you might keep using the old ones at home but if you're going out on the road, you take the young strong ones.
Of course the electronics inside the zmax could possibly fail eventually.
The nemesis is just a mech mod; physical bottom switch; adjustable centerpin; a mech mod just holds the battery and maybe you can buy electronics separately, but there's not much choices/variety of electronics available for mechs at the moment.
Basically with a mech there's not much that can fail; (there's much that can 'go wrong' in an ouch sort of way, but there's not much that can fail).
I've of a vamo3, a zmax, and a chiyou(mech) which all use the same M21x1 threading, so I can (and do) swap pieces around between them.
If I bought a nemesis, I couldn't do that because it uses a different thread (m20x... 1?)