Bosch 24V Makita CXT Battery Adapter

I have an old 24V Bosch SDS Drill with a failed NiCad battery.  Rather than rebuilt the existing battery I designed an adapter to hold two 12V Makita CXT batteries.

The pictures show an earlier design, this design brings out all the connections from the battery to allow a 3S BMS to be fitted for each battery.

WARNING:  The Makita CXT batteries do not appear to have built in battery protection, hence you will destroy them if you over discharge them.  It is recommended that you fit 2 BMS as part of the build, one for each battery.

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The terminals are designed to take standard 6.25mm blade crimps, although these are an interference fit they should be glued in place with either a hot glue gun or epoxy.

Wire the connections to the BMS and then wire the BMS outputs in series to give 24V.  I wired this in 1.0mm^2 wire.  The drill will draw 15-20A so make sure your wiring is suitably rated.

WARNING:  The Makita batteries can output a significant amount of power, check your wiring carefully before connecting the batteries.

The connection labelled T appears to be a thermistor for the battery, however this has not been tested and there is little information available on the build of these batteries.

The battery holders are mounted using heat-set inserts.

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Other Hardware:

• 4 x M3 x 8mm
• 6 x M3 x 16mm
• 6x M3 Hex nuts