Bosch FUG10A Replacement Battery 7.2V 1000mAh B5870

Bosch FUG10A / FuG13a — 7.2V Ni-MH Replacement Battery (B5870)

This is a 7.2V, 1000mAh Ni-MH battery for the Bosch FUG10A and FuG13a portable two-way radios. It replaces OEM part numbers B5870, B5870GRX, and 8697322951. Voltage and capacity match the original pack exactly.

• FUG10A and FuG13a platform fit: Both radios share the same 7.2V battery bay, connector pinout, and BMS handshake protocol — one pack covers both models without modification.
• Bench tested on actual hardware: We cycled this pack through transmit loads on the FUG10A bench rig. The BMS held stable under sustained PTT draw and did not trigger overcurrent cutoff during normal push-to-talk bursts.
• First insertion into the FUG10A dock: If the charger shows a fault LED on first insertion, remove the pack, wipe the contact strip with a dry cloth, and reseat firmly. The dock requires a clean contact cycle to complete the BMS handshake before charging begins.

Why the FUG10A cuts out mid-transmission on a freshly inserted battery

Ni-MH cells ship at storage voltage — typically around 1.1–1.2V per cell, which puts a six-cell 7.2V pack near 6.6–7.2V before any charge cycle. Under transmit load, that lower starting voltage can dip enough to trip the radio's low-voltage cutoff momentarily. This is not a faulty pack. Run the battery through one full charge cycle before first use and the cutoff threshold clears on subsequent transmissions.

Bar indicator showing one fewer bar than expected after fitting the B5870

The FUG10A reads battery level using fixed voltage thresholds, not a fuel-gauge chip. A new Ni-MH pack at storage voltage sits below the top threshold, so the radio displays one bar short of full even though the cell capacity is intact. Charge the pack fully — the dock green LED confirms completion — and the bar indicator will read correctly at the next power-on. If it still reads low after a full charge, check dock contact continuity first; a dirty contact strip causes incomplete charge termination and leaves the pack at roughly 7.0V instead of the expected 7.2V.