It also looks like there is a 3-pin standard JST charging connector (one wire for each cell plus ground).
The black part would be standard wrapping. Hard to know if there’s a protection circuit inside. You should be able to send the specs to a battery manufacturer and have them crete a custom pack for you. It might cost a bit more than if you created it yourself, but they might be able to get you the right connector etc.
If you want to create the pack yourself, there are a number of guides online, but the connector becomes the issue; you might need to look through pages and pages of Digikey connectors to spot the exact model (wish I knew it - maybe someone else here does).
I did an google search and apparently the plug is called “sm”. And indeed, when I search for “18650 sm 7.4” on AliExpress for example I see the exact battery pack that you need.
I would personally look into lipo or other batteryies of low discharge. Those batteries are usually used to control brushless motors and such for drones who need a lot of amps for control of high amperage motors. I would look into low discharge lipo batteries or other kinds like NiMh batteries because you will be able to longer usage out of your bot. Good luck!!!
