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You could charge it by connecting a bench supply set to 43.4V and turn the current down to 500mA. This could take a few hours to charge. It is charged when the current falls off to near zero.

I did a Honda CRF250R conversion with 400 of these A123 cells, and built a custom balancing charger for it as well.

It looks like what you are going to get is a 12S8P pack. 12 series packs of 8 cells in parallel. The 40 volts comes from 12 x 3.3V nominal for these cells. Full charge is 3.62V/cell or 43.4V for the pack.

The posting also says "commercial grade BMS" which is a "battery management system". This usually means each pack (a pack being 8 cells in parallel in this case) has a circuit across it that shunts current around the pack when the pack is full ie. 3.6V. This way, you put a charging current through the whole pack and each pack in series will top off. If it has this type of BMS, the pack will clamp charging voltage to around 43.4V assuming you have the charge current limited. If the voltage continues to climb past this, then it does not and turn the power supply off if it gets to 45-46 volts. Put a load on the pack to get the voltage back down to 43 volts or so.

The other possibility is that the connector merely brings out the voltage for each cell, and connects to a BMS that is part of what the pack plugs into. If this is the case you could use a LiFE charger that can do 12S packs and wire into the connector and that will balance the cells.

Be careful with this thing! 40V prob not going to kill you but you could start a pretty big fire in no time at all not to mention burning the crap out of yoursellf. My experience with the packs I made was not without incident!
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