Changing batteries in the Cateye Loop is extremely easy, but only once you know how.  I tossed the packaging the day I got it, and I don’t see instructions online, so I had to figure it out for myself.  If you’re having trouble getting it apart–since it’s not at first obvious–then follow the instructions below.

First, grab a flathead screwdriver.  I took the headlight off my bike while I did this, but you an just as easily leave it mounted.

Next, carefully slip the end of the driver between the dome that covers the light, and the rest of the body.  Twist the driver a little, and the dome will begin to pop off.

Once the dome is off, grab the LED and pull up.  The batteries are held inside a casing directly under the circuit board.

Slide the batteries out–the casing is open on one side only–and then slide some new ones in.  Assemble it in reverse order.

The Loop uses (2) CR2032 watch-style batteries.