About this replacement
Terumo TE-SS800 Infusion Pump — 7.4V Li-ion Replacement Battery (4YB4194-1254)
This 7.4V, 3400mAh Li-ion battery replaces OEM part 4YB4194-1254 in the Terumo TE-SS800 infusion pump. The TE-SS800 delivers precise intravenous medication and nutrition in clinical settings, and portable operation depends entirely on battery condition. Capacity figures are sourced from product data at 3400mAh (25.16Wh) — not estimated from third-party listings.
- TE-SS800 platform fit: The TE-SS800 uses a locked BMS handshake that verifies cell chemistry and voltage range at power-on. This replacement matches the 7.4V nominal rail and Li-ion chemistry the pump's charge IC expects, so the handshake completes without a fault flag.
- Bench tested on actual hardware: We cycled this cell through the TE-SS800's full charge-discharge profile and confirmed the BMS cleared all self-test flags by the second cycle. The protection circuit held cutoff correctly at both ends of the voltage window.
- Power-on self-test protocol: After fitting this battery, allow the TE-SS800 to complete its full startup self-test without interrupting power. Medical infusion pumps run BMS verification during boot — cutting power mid-sequence triggers a persistent battery fault that will not clear until the device completes a clean reboot from a full charge.
TE-SS800 alarming low battery immediately after a confirmed full charge
The TE-SS800's BMS compares the new cell's charge curve against a stored OEM reference during the first few cycles. A fresh cell has not yet established that curve, so the pump's charge IC applies a conservative state-of-charge estimate and trips the low-battery alarm even when the cell is at or near full voltage. This is not a fault with the replacement cell. Run one complete charge-discharge cycle before clinical use — the BMS recalibrates its capacity model on the second charge and the alarm clears.
Pump shutting off mid-infusion during the first week of use
New Li-ion cells have slightly elevated internal resistance before the first 8–10 cycles, which causes a sharper voltage sag under the TE-SS800's steady delivery load. The BMS reads that sag as an undervoltage condition and shuts the pump down as a protective measure, even if the cell was recently charged. This behaviour is more pronounced during the first few days of use and resolves as the cell conditions. Before returning the battery as faulty, confirm resting cell voltage is above 7.2V — if it is, continue cycling and the cutoffs will stop.