Connect the red wire from the 10cm tail to the red wire inside the base, black to black, then leave the Anderson connector outside the base.
Screw back the base.
You can ride the bike with the bottle battery as before while waiting for the lipo packs.
When you get the lipo packs, make up the second 5AH battery.
Charge the lipo packs to 41V (20.5V each).
Then take the bottle out, plug the new pack into the Anderson, test the bike.
If everything is OK, charge the bottle and put the bottle back in.
Then take a deep breath, switch on the bottle battery.
This is the moment where the lipo pack can damage your bottle battery because bottle batteries are usually fitted with a FET based soft switch. The flow between the two batteries can kill the soft switch.