Sumitomo BU-25 Type-25 Replacement Battery 11.1V 2600mAh

Sumitomo Type-25 / Type-25e Fusion Splicers — 11.1V Li-ion Replacement Battery (BU-25)

This is a 11.1V 2600mAh Li-ion battery for the Sumitomo Type-25, Type-25e, and compatible BU-25 fusion splicers used in fibre optic splicing and field survey work. It slots directly into the battery compartment and connects to the instrument's onboard charge management circuit. Capacity matches the original BU-25 specification at 28.86Wh.

• Type-25 and Type-25e platform compatibility: Both models share the same 11.1V three-cell Li-ion architecture, battery form factor, and BMS communication protocol. The connector pinout and charge termination signal are identical across the platform, so one pack covers both variants.
• Bench tested on actual hardware: We ran this pack through charge and discharge cycles on a Type-25 unit. The BMS accepted the charge handshake immediately, and protection circuits responded correctly to arc motor load spikes during simulated splice cycles — no false cutoffs triggered.
• Post-install calibration before field deployment: After fitting this battery, run a full calibration cycle through the Type-25 instrument menu before heading to site. The splicer maps battery state during calibration, and skipping this step causes premature low-battery warnings mid-session — especially on the first splice run of the day.

Arc motor current spike tripping BMS during splice cycle

The Type-25 arc discharge motor pulls a sharp current spike at the moment of arc ignition — typically the highest instantaneous draw the splicer makes. On a partially depleted or newly installed pack, this spike can push the BMS protection threshold and trigger an immediate cutoff. The result is the unit shutting down at the exact moment it should be splicing. Letting the pack charge fully to 12.6V before the first arc cycle gives the BMS the headroom it needs to absorb that spike without tripping.

Type-25 shows battery error or won't recognise pack after sitting unused

A Li-ion pack that has sat unused for several months can self-discharge below the BMS recovery threshold — often under 9V per cell group — causing the protection circuit to enter sleep mode. When the Type-25 sees no valid voltage signal from the pack, it displays a battery fault or simply refuses to power on. Place the pack on the Sumitomo charger and leave it for at least 30 minutes without interruption — most BMS circuits will wake and accept a charge once the recovery pulse brings cell voltage back above 2.5V per cell. If the charger LED does not change state after 45 minutes, the pack has not recovered and should be replaced.