It's a very common, standard battery.

It is used in many watches, calculators, remotes, keyless-entry remotes, etc. You can find it at any electronics store, jewelry store, and many grocery stores in fact.

As with any watch/calculator battery, you go by the number on the face of the battery, in this case "2025". You'll see it sometimes labeled as CR2025, BR2025 or something similar, depending on the battery manufacturer.

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Tony Fabris