I wanted to replace my SLAs on a Wilderness Energy kit with something more decent. I have managed to put 4 DeWalt packs in parallel (for range) using a single BMS module for both charging and low voltage and overcurrent cut-off.
The BMS has a 15A fuse, but it also has a switched output that the DeWalt tools use. The FET on that port is a 70A part, but there is a current sense resistor as well, and I don't know what the maximum current is before the cut-off is triggered. I measure 25A on the discharge, which is exactly the same I used to get on my 36V SLA system under full load, so I don't think there is any influence from the BMS. I wish I had a load that could take more than 750W even for short periods to test this, but I really have no clue what I could use.
I wired the 4 packs in parallel, connecting all balancing connectors together as well. (Thanks for the connectors Brian :) ) I also removed the DeWalt connector from the charger and used a standard circular connector so I can use a few feet of cable between the charger and the battery pack. When the charger is unplugged I slip in another circular connector that has a few wires and resistors to turn on the battery output. I found two links very useful:
I have now run the bike for a couple of weeks. I have a short commute (just a couple of miles each way), but I have a climb of several hundred feet at the end (which is why I wanted an E-bike in the first place). The stock DeWalt charger (well, except for the cable) has no problem with the custom pack, and I am very happy that I don't have to worry every time if the charger will accept my pack since the discharge is controlled by the BMS. (It really is the BMS that makes the decision if the pack is bad, the charger just queries the BMS.)
I am happy to say that I avoided killing any of the BMS modules since I was very careful to disconnect the balancing connectors first, then the positive side, then the negative side. During re-connect the most important thing is to start with the negative side first. I always connected positive next and had no problems.
All in all I am really happy with the system! }:)