Which portable batteries fit in TimePorter?

Generally, anything less than 4-inches long, and less than 1-inch in diameter will fit. How much space is left, of course, depends on which battery you choose, but all the batteries listed below leave enough room for your cable and a USB charger plug.

Mophie power reserve 1X
www.mophie.com/shop/universal-batteries/power-reserve-1X

Anker PowerCore mini
www.anker.com/products/A11040B1

Jackery mini
www.jackery.com/jackery-mini/