How is the GA-B2100 different from the GA-2100?

It adds Tough Solar charging and Bluetooth smartphone link to the same slim octagonal case. The original GA-2100 runs on a standard battery and has no app connection.

Does it need a battery change?

It uses Tough Solar, charging from light through the dial. In normal use the rechargeable cell lasts years without a swap, though very dim storage can drain it.

Is it good for swimming?

Yes. It is rated to 200 m water resistance, which covers swimming and showering. Casio does not rate it for scuba diving.

What does the Bluetooth link do?

It syncs the time with your phone through the Casio Watches app and helps set alarms and other settings. It does not add notifications or fitness tracking.

How does it fit on the wrist?

The case is noticeably slimmer than standard G-Shock models, so it sits flatter and fits under sleeves more easily. The resin strap runs long, so smaller wrists may need a tighter hole.