I'm buying an XM-3500li and adding an additional 4 cells for a total of 24 cells. I need a good and inexpensive BMS to maintain the batteries. I've heard lots of talk about the goodrum/fetcher BMS, but I can't find one for sale anymore.
Rechareable Lithium Power has a ready-to-use one for $230, but they're out of stock.
TPpacks has the bare circuit board with a list of components that you need to buy and solder yourself, but they're also out of stock.
I would prefer to buy a premade one, but I have the skills to build it myself if necessary. Does anyone have a link to a place I can buy one?