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Model guide · Reviewed

G-SHOCK GA-B2100 “Solar CasiOak”: Size, Battery Life, Water Resistance & Specs

Short answer

The G-SHOCK GA-B2100 is the solar-powered, Bluetooth version of the octagonal GA-2100, at 11.9 mm thick and 52 g.

Thickness
11.9 mm
Weight
52 g (1.8 oz)
Water resistance
200 m / 20 bar
Power
Solar, ~7 mo per charge

Casio added Tough Solar charging and Bluetooth smartphone link to the CasiOak shape in 2022. The GA-B2100 is only 0.1 mm thicker and 1 g heavier than the GA-2100, and it syncs time automatically with the CASIO WATCHES app. On a full charge it runs about seven months in normal use without light, or about eighteen months stored in darkness with power saving on.

GA-B2100 specifications

Casio's specifications for the stock GA-B2100-1A. Custom builds can differ; see the notes below.

G-SHOCK GA-B2100 specifications
ReferenceGA-B2100-1A
Module5689
DisplayAnalog-digital
ShapeOctagonal
Case size (L × W × H)48.5 × 45.4 × 11.9 mm (1.91 × 1.79 × 0.47 in)
Weight52 g (1.8 oz)
CaseCarbon fiber–reinforced resin (Carbon Core Guard)
BandResin
Band fits wrists145–215 mm (5.7–8.5 in)
Water resistance200 m (660 ft, 20 bar)
PowerTough Solar (rechargeable): about 7 months of normal use, about 18 months in darkness with power saving on a full charge
Tough SolarYes
Multi-Band 6 (atomic time)No
BluetoothYes (CASIO WATCHES app)
LightDouble LED (dial and LCD)
Launched2022
Casio U.S. list price$165

Features

  • Tough Solar charging
  • Bluetooth time sync with the CASIO WATCHES app
  • About 300 world time cities in the app
  • Phone finder
  • World time (38 time zones)
  • 1/100-second stopwatch
  • 60-minute countdown timer
  • Power saving

What is the G-SHOCK GA-B2100?

The G-SHOCK GA-B2100 is Casio's octagonal analog-digital watch with Tough Solar charging and Bluetooth, launched in 2022. It keeps the GA-2100 “CasiOak” design and uses module 5689.

How long does the GA-B2100 last on a charge?

A fully charged GA-B2100 runs about 7 months of normal use without light, or about 18 months stored in darkness with power saving on. Regular light exposure keeps it running indefinitely, because Tough Solar recharges its battery from any light source.

How big is the GA-B2100?

The GA-B2100 measures 48.5 × 45.4 × 11.9 mm and weighs 52 g, according to Casio. That is about 0.1 mm thicker and 1 g heavier than the battery-powered GA-2100.

Is the GA-B2100 waterproof?

The GA-B2100 is rated 200 m (660 ft, 20 bar) water resistant by Casio, which covers swimming and showering. Like other G-SHOCKs outside the Frogman line, it is not an ISO-certified dive watch.

What does the GA-B2100 Bluetooth do?

The GA-B2100's Bluetooth link connects to the CASIO WATCHES app to set the time automatically and adjust the watch easily. Casio also lists about 300 world time cities, a time and place log and a phone finder.

Is the GA-B2100 an atomic watch?

No, the GA-B2100 does not receive radio time signals (Multi-Band 6). It gets accurate time from your smartphone over Bluetooth instead, so it needs the CASIO WATCHES app to sync.

What module is in the GA-B2100?

The GA-B2100 uses Casio module 5689, printed on the case back. Casio's module 5689 manual explains charging, phone pairing and every mode.

How much does the GA-B2100 cost?

Casio's U.S. list price for the GA-B2100-1A is $165, as recorded by G-Central, which is $55 more than the GA-2100-1A1. The difference pays for solar charging and Bluetooth in the same case.

Is the GA-B2100 right for you?

The GA-B2100 suits

  • People who like the GA-2100 shape but never want to replace a battery.
  • Travelers who want automatic time from their phone and about 300 world time cities in the app.

Look elsewhere if

  • Anyone who wants the lowest price in the octagonal line — the battery GA-2100 costs less.
  • Buyers who want radio-controlled atomic time without a phone — the GA-B2100 syncs over Bluetooth, not Multi-Band 6.

Custom GA-B2100 builds: what changes

  • We build primarily on the GA-2100; ask us before buying a GA-2100 bezel for a GA-B2100, since accessory fit is listed per model.

Bezelwright is an independent customizer and is not affiliated with Casio. Specs above describe Casio's stock model.

Sources

Figures describe Casio's stock reference model. Independent references are used where Casio's own page could not be read directly, and cross-checked against Casio's published specs.

  1. Casio (U.S.): GA-B2100-1A specifications (official Casio, accessed October 25, 2026)
  2. Casio (UK): GA-B2100-1A1 specifications (app features, band size) (official Casio, accessed October 25, 2026)
  3. G-Central: G-SHOCK GA-B2100 specifications (independent reference, accessed October 25, 2026)
  4. G-Central: G-Shock GA-B2100 with Tough Solar power and Bluetooth link (independent reference, accessed October 25, 2026)
  5. Casio G-SHOCK (UK): How do solar powered watches work? (official Casio, accessed October 25, 2026)
  6. Casio G-SHOCK (UK): Are G-SHOCK watches waterproof or water resistant? (official Casio, accessed October 25, 2026)
  7. G-Central: G-SHOCK GA-2100 specifications (independent reference, accessed October 25, 2026)