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Two batteries on each side of the compartment seemed to work.
BMS Board
2S 2-3A 5-8.4V Red
Size: 62 x 26 x 6.9mm
Charging Voltage range: 8.40-8.45V ± 0.05V
Over-discharge Voltage range: 4.6-5.1V ± 0.05V
Maximum operating current: 2-3A
Maximum instantaneous current: 4-6A
Working temperature: -40 ~ +50°C
Resistance: less than 45mΩ
Wired the leds on the BMS to the original circuit board led. Removed all components from the original board except the power plug and battery led.