We have a couple of threads exploring the EGO series of 56V yard tool packs for Ebike and other uses here on ES. There are some builds using these packs. We have a design for a 3D printed connector that is in the prototype test phase. These are 14S packs which are a good fit for 48V systems. Maximum full charge voltage is generally a little under 58.8V using the EGO chargers. Makers of 14S Ebike batteries call them 52V or 50V whereas EGO calls them 56V, which is about their resting voltage after sitting fully charged. They reportedly have timers in the packs to drain them down to storage level after 30 days, but some people have reported that their packs don't seem to do this. There is a clock chip in the BMS, perhaps for this function.
In many tool packs (including the EGO 56V) there is no BMS hardware protection for overdischarge. The tool is generally responsible for providing this feature, so it is not integrated into the pack BMS hardware (no FET power switch). At least on the EGO pack the four pins are for negative, positive, temperature (thermistor) and data communications with the BMS. The data communications format has not been looked at, but that would be a good small project for someone. Without that the low voltage cutoff in the controller must be used to protect the pack against overdischarge.
The BMS is engaged by the charger and apparently provides cell level balancing.
Many tool packs are not designed for high current and will get hot or even overheat at Ebike current levels. EGO packs have better cooling design than most others I have looked at. The EGO battery powered yard tools are also fairly good so the batteries can be a true multi-use item. We are starting to see discounts from some sources on the battery packs. The battery packs carry a 3 year warranty that can be accessed via local hardware stores so that can be of some value.
More information here:
https://endless-sphere.com/forums/viewt ... 14&t=93563