DR600 Li-ion battery pack was taken apart and a battery management system (BMS) was added to it. This was not very easy, but not too bad either having equipment, materials and experience with this sort of thing. If you are going to do something like this, please be very careful. Don't try this if you don't know what you are doing.
Li-ion pack for Roland V-Accordion investigation: https://youtu.be/1obxLWO8zo0
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https://www.youtube.com/watch?v=a600wjWiT0g