Open the battery and peal back any heatshrink or tape to get full access to the BMS, then unplug the power wires and pull out all the connectors. Purchase a Chinese BMS and solder on the charge and power wires. The connector for the 10 sense wires most likely won't fit, so you'll have to cut it off and solder the one that comes with the new BMS being careful to get the correct connection sequence shown on the diagram that comes with it. Reassemble the case, then you have a battery that you can use with anything. Your old charger won't work, so you have to buy a standard one for about £12.
The terminals on the battery won't be much use, so it would be better to drill a hole and run the power wires to an external connector. Also, the Chinese charger won't have the right connection, so drill another hole in the case and add a standard 5.5mm jack socket and solder the charge wires there.
It sounds like a lot of work, but as long as you can solder and measure voltages, it's fairly straight forward.
Here's a picture. Basically, you can chuck everything on the left, leaving the cell-pack with its red and black power wires and the multipin sense wire connector. It's those nasty thin green, yellow and white wires bottom left that stop you from using the battery as is.