The Surface Pro 3 actually has 3 batteries in it, in case you forgot.
It has 1 AAAA Alkaline Battery that powers the pen itself which most people know about, but it also has 2 watch batteries that power the “Purple Click” button that initiates OneNote.
These batteries are #319 Button Cell Silver Oxide Watch Batteries. You can purchase backup batteries here:
- AMAZON: 10 SR527SW 319 Battery Energizer Watch Batteries ($8.03 w/ Free shipping)
http://www.amazon.com/gp/product/B000OVNLQA/
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