get a new battery. most of the lasers use L-ION batteries and the are designed different that your good old Alkaline battery. Think of them like a marble rolling across a table, when it hits the edge it pretty much drops straight down. That's how a Iithium Ion battery operates.Last year I bought a BG380 with the integral laser. The laser was cool and honestly at longer ranges I was able to shoot much better with it. However the laser quit working about 3 weeks after I bought it. I haven't sent it back to get fixed and honestly I don't miss it one bit. I really wish they would sell it with a small led light instead of the laser.
When I first got my Sig P238/laser combination, the packaged laser did not work, I checked the voltage with a tester and it only read about 1/2 volt low so I called Sig support and they asked me to pick up and try another battery before sending it in. I got a new battery and it works just fine.
The arming button on many of the cheaper lasers ( if they advertise it as a free or small additional cost enhancement, it is cheap) can be accidentally turned on when holstering or storing the weapon and thus the short lifespan of their batteries.
Al