I have the same light except it is the M20s S2 model I bought about 3 months ago. Mine will not lock out. I was able to fix one of the biggest complaints of the M20s which is the little side button is almost impossible to find in the dark, with gloves on or without looking. I ordered the a M30s tailcap. This tail cap allows me to tail stand the light and it's much easier to find the side button.
As far as battery life, this is what I have found. When I first got the light I bought some cheap Ultrafire 3000 batteries thinking they burn longer because of the high mAh rating. They were also very inexpensive and I didn't know better at the time. You can imagine my concern and disappointment when I was only getting 1.5 to 1.75 hours run time on high mode. I called Olight USA and spoke to one of the high ups over there about my problem. He said it was a battery issue and with the right batteries I should be able to get 4 hours run time on high mode. I ordered some different batteries and this is the results of my testing.
Ultrafire 3000. 1.5 to 1.75 hours. I even had one battery that only gave me 1hour and 20 minutes. These are the worst batteries I have bought or tried.
Trustfire 2400 Gray. 2.5 hours or maybe just a little more.
Trustfire 2400 Flame Wrapper. 3 hours to 3.25 hours.
AW 2900. 4 hours 10 minutes.
Redilast 2900. 4 hours 5 minutes.
Callie Kustoms 3100. 3 hours and 55 minutes. I need to cycle these batteries a few more times and see if I get a little better run time. These batteries have not been completely broken in yet and I should get a little better run time after a few charges.
I also noticed that the light stayed much cooler when running the AW, Redilast and Callie Kustoms than the other cheap batteries. Also, with these three quality batteries, I didn't notice any loss in the brightness of the light until after about 3.5 to 3.75 hours. I then started to notice the light begin to dim slightly but it still had plenty of brightness. At around 4 hours the light began to dim quickly until it shut down to a lower mode.
All in all I am very pleased with this light. It's still my favorite light, and probably the toughest light I have ever owned. I have brighter lights, longer throw lights and lights with more flood but my M20s does more things good than any of my other lights. It has more than enough brightness and throw while still giving plenty of spill. UI is very simple. I have not found anything that can match it in battery run time.