the free Efest from toddcshoe are Great!
here is an S1 review that has an Efest runtime test on the S1
I just bought the 1200 mAh Keepower 18350 from illumn, yesterday.
Ive been running 650 mAh 16340 Protected ICR cells until now.
unrelated to 18350, I took a photo of one of their display cases…
afaik There is no Protection Circuit built into the S1, and the IMR batteries are UnProtected.
So I wont have the safety net of overdischarge protection, but,
I check my batteries on a voltmeter every few days
In my limited EDC use pattern, the 650 mAh battery goes below 3.7v (half empty) in about 4 days,
so Im expecting the 1200 mAh IMR (Keepower) will last about a week… we shall see 
Im a little nervous about flying without a seatbelt (Protection Circuit)
otoh, I think its cool that the new 1200 mAh battery has almost double the capacity of the 650 mAh 16340 I had been using.
and I also think its cool that you just inherited some 700 mAh IMRs (Efest)
Congrats on your new light!