Hello,
There are 6 screws on the back of the light where the switch is and uder there is a battery which is replaceable.
Please see correct battery below:
https://www.thesolarcentre.co.uk/products/SolarCentre_18650_2600mAh_Lithium_Ion_Rechargeable_Battery-857-5.html
Hi, They are IP44, the USB port is protected by a rubber seal, yes you will need to remove the lights for USB charging, Fixings are supplied.