Laser is not staying on. Any idea??

I have a 2W blue laser. It's about 10in long.
It takes 2 3.7V batteries.
When I put the batteries in correctly and press the on button, the laser may or may not turn on.
When it does it's fine, but when I turn it off and try to turn it back on, it won't come on.
I usually have to keep twisting the button cap off and putting it back on for it to come on again.
Batteries are fully charged, idk why this happens.
Do I need a new spring? A new button cap? Please help

Use a piece of foil or a wire to connect the battery to the host threads without the tailcap on, if it turns on it is a tailcap issue, in which case, take the tailcap wrap and put it back together, if that doesn't fix, you will probably need a new one.

I think it's the tailcap issue, which you can, luckily, easily fix.

Look into the tailcap, you should see a retaining ring with two holes in it, something like this:

[Not tailcap, but good image of two holes on the sides]

Grab tweezers, or screwdriver or a really sturdy pen, and try to rotate this ring clockwise. It should tighten it, like it was before, and fix the problem.

Like this: