Laser in daylight to photocell

For a university club project I need a laser that will noticeably affect a photocell in daylight from ~20ft. The photocell is in a small enclosure, but it still gets a fair amount of light from the surroundings. Right now I am using a very cheap 5mW (apparently) red pointer, and it is so weak that it is nearly impossible to aim at 20ft, and it does not raise the photocell output enough.

From looking around on these forums I have decided that something in the 30-50mW range would be good, and green would also be good as it would be easier to aim. Would that power level likely not damage a photocell? I would definitely need to avoid that.

The other big issue is I would like at least 30min uptime as we will be running tests for ~20 minutes at a time and it would be impossible to turn it off between each test. I looked around on laserbtb, o-like and lazerer, and quite a few did not specify operating time. It will also need to be battery powered.

Does anyone have any insight for me? We are on a fairly tight budget so the lower the cost the better (something in the $50 range would be great if possible), but I would also like something somewhat reliable. :thanks:

EDIT: Found this one that would work with a portable USB battery, but no uptime info