The pocket bridge power banks use 18650 Li-ion rechargeable batteries rated at 2600 mAh each.
If you need to replace your battery, they can be purchased from any number of suppliers online. We do not often buy them in small quantities, so have no recommendation for a specific source. You can trying searching Amazon or elsewhere for “18650” - be sure to search for protected li-ion batteries.
This is also written on the battery in the power bank - which can be accessed by unscrewing the cap at the base of the power bank.
If you don't have a pocket bridge already and would like to order one, you can find them on our site here: https://flowtoys.com/products/pocket-bridge?_pos=1&_sid=2740979b6&_ss=r
If you do have a pocket bridge and need to order a replacement power bank, please email us directly at info@flowtoys.com