Dock port or what ever. Do not use a charger that has an amperage higher than 2.5. Lithium batteries are great but do not last if you charge then at high amps. For example, charge the Surface regular or pro at 4 amps and you will shorten the life of the battery by a high percentage. The percentage can be as high as 75 % if the amperage is much higher. I charge my cell phones with a Samsung charger that lists .7 amps. The battery at that amperage should last as long as the phone. But charge it with a fast 2 amps charger and the battery may only last several months. Do a search on "lithium battery life" for more details.