Yes, I'm frustrated with Olights... I got 2 S1's, one S15, and one S30 - all pretty useless to me. I guess I was over estimating my modding skills, think'n I could get them apart and fix up the UI, tint, and power, but, they are nothing but trouble...
For the battery - Yes, it's a button top. Did you order the 5C tint? I measured lumens for all modes in my PVC light box. #'s across the board are lower, including the ultra low mode.
For the 5C tint using a fresh EFEST V2 550 @4.20v:
Ultra low: 2.3 lumens, low: 114 lumens, med: 224 lumens, hi: 456 lumens, turbo: 658 lumens
I'm think'n the 5C is not a U2 bin, but probably a T6 at best, more likely a T5 and that explains most of the lower readings.
I was able to pop out the pill - not difficult to do. A couple of light taps on a plunger (syringe plunger from a solder paste needle) from the tail and the pill assembly pushed out the top, after removing the bezel and reflector as freeme did, earlier posted.
Bad news is there's not much space, because the switch is mounted on a vertical PCB, and the diameter of the driver is pretty small. Piggybacking, maybe a 12 mm driver would fit. Good news is I do have 10 mm MtnE FET driver boards and a couple parts kits for the 10mm baords, so it's certainly do-able with what I have on-hand.
Also of note, they used thermal grease under the star with a screwed down reflector -- potentially bad combo, along with sharp edges for the wire holes. Mine had a tear through the LED+ wire at the point it passes through the pill top - potentially bad ground out could happen easy. The wires are either 26 or 24 AWG and 150C rated, not the better 200C wires we use. I'll take the sharp edges off the holes (using an xacto), and replace or cut down the wires before re-assembling. The side button is simple and will not get damaged from removing the pill - unlike the Olights.