Problem using 2 batteries but not 1?

[Dknights]

Exactly what the title says. My laser only works with 1 battery but not 2? So the power rating is half what it normally is. I have the option to use one battery but that’s not near as fun It’s a high powered laser, somewhere between 500-1000mw and the batteries are 18650. I’m kind of stumped why this would happen. Any insight would be appreciated. It IS an eBay laser, which is probably relevant. Blue laser.

 

[Snecho]

It would be a lot more helpful to see the actual laser in question.

 

[Anthony P]

Sounds like a button top (or lack there of) battery issue. Like Snecho said, need more info.

 

[BowtieGuy]

Like Anthony mentioned, if you're using flat top batteries, you may have a connection issue.
You could try some button top batteries, or try to use a small neodymium magnet as a spacer between the cells.

 

[Snecho]

It also sounds like you're trying to use an
18650 instead of two 16340s which cheap eBay blues tend to use.

But again, I'm just spitballing here as the original post is very confusing.