Duncan,
Yes, it could be the batteries packed with your laser.
They may be of insufficient capacity or just plain old.
Use only fresh Lithium batteries.
Lasers don't like the cold, anything lower than about 12C makes the beam fade.
If you're hand holding the laser, I suggest that whilst not being used it's kept in your pocket where it's kept warm by your body heat.
If it's mounted on your scope, you will have to gently heat the laser body to help keep the laser operational, this can be done with a eyepiece dew heater.