Why does my Ultrafire U20 turn off on high?

I used my Ultrafire U20 R5 as a headlight for my bicycle. It shuts off by itself when it is on High mode after about a minute. It does not seem too be too hot, only warm. Vibration does not seem to be the problem as I gave it a few good knocks with my fist and it did not shut off. I am using 3 year old Trustfire blue 14500 cells. How can I fix this problem?

Maybe protection on the batteries kicks in?

Thanks Shadowww for your reply. Why would the protection kick in? I have not modified this light.

I am a newbie. With that said, could it be the looseness of the battery in the chamber? Battery loses contact for a fraction, the circiut board thinks it is a mode change.. they say putting tape on the battery for a tighter fit might help..

Just sayin,

Sounds like the protection circuit shutting off. Depending on how many cycles they've been through, three years is getting on a bit for cheaper li-ion cells.

Hi Psion...I had this same thing happen last night with my FandyFire HD-2010 while using it on high mode, all other modes worked perfectly. I was using a Genuine Trustfire Flame 2400mAh battery fully charged to 4.2v (1x18650 in a sleeve).

As others have mentioned, likely it's simply the protection kicking in, as what happened to me with my Fandyfire. Try a different higher capacity battery, or perhaps just a newer battery. Chances are that should solve the problem.

Thanks for all the advice! You guys are awesome

Taping to get a tighter battery fit is a good idea. Especially with the vibrations that occur during cycling.

I does look like protection kicking in. I have 6 Trustfire blue cells freshly charged. Only 2 cells do not shut off on high mode. Looks like the other 4 cells are getting weak.

I shall order a couple of recommended cells from the battery section.

Get some xtars for it or panasonics

The Trustfire flame 14500s pack a punch you shouldn't have a problem tripping protection on these and they hold almost 800mAh.

I got mine from DX.

Were did you find Xtar 14500s I can't seem to find them?

Me neither. Looked all over..