Seiko and Casio Watch Battery Guide: Which Battery Does My Watch Take?

The quickest way to find the right battery for a Seiko or Casio watch is to use the number the maker has already given you. Seiko marks each watch with its calibre, and Casio marks each watch with its module number. Once you have that number, the battery is easy to pin down. This guide shows you where to find it, lists the batteries used in some popular Seiko calibres and Casio modules, and links you straight to the genuine Japanese batteries we stock. If you already have the old battery in your hand, our watch battery size chart will match its number to every equivalent in seconds.

Which battery does my Seiko watch take?

Turn the watch over and look at the caseback. Most Seiko watches carry a code such as 7N43-9080, and the first four characters, in this case 7N43, are the calibre. The same calibre number is also marked on the movement itself. Seiko's instruction manual for each calibre names the battery it uses, and the table below gives some examples taken from those manuals.

Across the wider Seiko quartz range, SR626SW (377), SR920SW (371) and SR621SW (364) are among the batteries you will meet most often, but sizes vary from calibre to calibre, so always confirm against your own calibre or the number printed on the old battery. Seiko automatic and mechanical watches do not use a battery at all, and Seiko Kinetic and Solar models run on a rechargeable cell rather than a standard watch battery. You can see all of our genuine Seiko watch batteries here.

Which battery does my Casio watch take?

On a Casio, look for a number printed inside a small box on the caseback. That is the module number, and Casio's operation guide for each module states the battery type. Many Casio digital watches use a 3 volt lithium coin cell rather than a silver oxide battery, so the module number really matters. The table below lists some well known examples from Casio's own guides.

Casio analogue watches more often use silver oxide cells such as SR626SW (377) or SR920SW (371), and the module number will tell you which. If the number on your caseback is not listed above, Casio publishes the operation guide for every module on its support website, and the battery type is given in the specifications section. Watches marked Tough Solar use a rechargeable cell that is not meant to be swapped for a standard battery.

Check the old battery as well

Whatever the calibre or module says, the most reliable answer is printed on the battery already in your watch. Makers sometimes change parts during a production run, so it is always worth comparing the number on the old cell before you order. Type it into the search box on our watch battery size chart and you will see every equivalent code, the exact size and the genuine Japanese brands we stock in that size.

Fitting the new battery

Many Seiko and Casio quartz watches can have their battery changed at home with a caseback opener and plastic tweezers. Note which way up the old battery sits, fit the new one the same way, and handle it by the edges. Some Casio modules also need a reset after a battery change, which is explained in the operation guide for that module. If your watch is water resistant, have the seal checked afterwards, and for valuable or diving watches a watch repairer is the safer choice.

Browse our full range of genuine Japanese watch batteries from Maxell, Murata, Seiko and Seizaiken.