Thanks! The cutout is with a 2.3ohm joye brand 510 atty at 4.15V and higher, loaded. The batteries seem healthy... they work fine in a single cell unregulated box... the two I tested with read 4.06V tested separately.
Chris, I have a 2.0 ohm atty on it now and it worked great from 3.99v to 5.5v measured under load and ONE 14500, 900mah Trustfire. AW would be better.
Also worked with a 1.7 ohm atty but didn't try a range. Set it to 4.08v just to try it.
A 1.3 ohm didn't work. Cut out due to overload. The 1.3 ohm worked good with ONE 18350, 800mah, same circuit.
So in-conclusion (IMHO), It's the battery that is causing the cut-off with your atty/voltage selection. Not enough ummph. LOL