Casio G-Shock GA-B2100-1AER review
The GA-2100 to buy if you never want to change a battery.
- Skip it if
- You want a mechanical watch to look at and look after
as of 6 Nov 2026, 13:25 GMT · Details
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.co.uk at the time of purchase will apply to the purchase of this product.We earn a commission if you buy through the retailer links on this page. It doesn't change our verdict. How we make money →
Researched, not used. We haven't used this product. This review is built from the maker's details and what other buyers report.
What we like
- Tough Solar charging, no routine battery changes
- Bluetooth link keeps time and world time correct
- Most convenient of the slim G-Shocks
Worth knowing
- Depends on the phone app
- Case is still fairly wide
Out of stock when we checked: our alternatives
Closest in size first, then by our score. None of them was showing out of stock when we last checked.
as of 6 Nov 2026, 13:25 GMT · Details
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.co.uk at the time of purchase will apply to the purchase of this product.
as of 6 Nov 2026, 13:25 GMT · Details
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.co.uk at the time of purchase will apply to the purchase of this product.
as of 6 Nov 2026, 13:25 GMT · Details
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.co.uk at the time of purchase will apply to the purchase of this product.ⓘ Some links are affiliate links: a purchase may earn us a commission at no extra cost to you. It never decides what we pick or how we rank it. Prices shown may have changed since they were checked.
Our review
The GA-B2100-1AER takes the slim CasiOak shape and adds Casio's Tough Solar charging and a Bluetooth link to a phone app. The phone keeps the time and world time correct, while the light-powered battery means no routine battery changes. It is the most convenient of the slim G-Shocks. The catches are the app dependence and a case that is still fairly wide.
What it is
This is the connected, solar-powered model in the GA-2100 family. The case design matches the standard GA-2100, with the octagonal bezel and carbon-reinforced resin, but it has an updated module and a few extra functions. It sits at the top of the basic CasiOak range, below metal-cased models.
The movement
It is a quartz watch with Tough Solar charging, meaning the dial acts as a light collector that tops up a rechargeable cell. Casio says a full charge lasts many months in the dark. Bluetooth connection to the G-Shock Connected app lets the phone set the time and adjust world-time cities automatically, as well as helping you configure alarms. It does not use radio signals, so it depends on a phone link for the self-setting. The rechargeable cell will eventually need replacing after many years.
It is easy to set up and works through the Casio app, but the app is basic and the link occasionally needs reconnecting after a phone update.
On the wrist
The case is about 45 mm wide and relatively slim for a G-Shock, so it sits flatter than the older bulky models. It remains a big watch on small wrists. The resin strap is light and soft, and the all-black treatment is easy to wear. It weighs very little for its size, which many owners like for all-day wear.
Water and everyday wear
It has a 200 m rating, suitable for swimming and showers, and the usual G-Shock shock resistance. The crystal is mineral. The LED backlight and lumed hands help in the dark. Bluetooth does drain a little power, but the solar charging keeps up for normal use if the watch sees daylight. If it is kept under a cuff all the time, make sure it gets some light now and then.
Against the alternatives
The Casio G-Shock GA-2100-1AER is the simpler battery model in the same shape. The Casio G-Shock GA-B2100CY-1AER is the same watch in a different colour treatment. For a solar watch without the phone element, the Casio G-Shock GW-M5610U-1ER is the radio-controlled square option. The Citizen Eco-Drive BM8479-09L is a very different solar watch with a more formal look.
Who it's for, and who should skip it
It is for people who want a modern, light and tough watch that largely looks after its own time. Phone owners will appreciate the automatic setting. Skip it if you dislike apps or do not want any Bluetooth, or if you want a mechanical watch. It is also not a dress watch, and the case is not small.
Pair it with a phone you already own and it is a very low-effort watch; without one, you lose the main advantage over the simpler model.
A researched review, built from the maker's specs, manual and Amazon.co.uk listing; facts checked 6 Nov 2026.
Who shouldn't buy this
Don't buy it if you want a mechanical watch to look at and look after: this runs on light and a quartz movement.
Key specs
| Movement | solar |
| Calibre | Casio 5689 |
| Case | 45.4 mm |
| Thickness | 11.9 mm |
| Lug width | — |
| Water resistance | 200 m |
| Crystal | mineral |
| Strap | resin |
| Power reserve | — |
| Accuracy | — |
This is a Researched review: we haven't used this product. We check the maker's details against at least two independent sources, re-check the price where we can track it automatically, and say plainly who it isn't for. Commissions never change a rating.