About this replacement
Mindray VS800 / WATO EX-20 — 11.1V Li-ion Replacement Battery (LI23S001A)
This 11.1V 6400mAh lithium-ion battery replaces the OEM pack in the Mindray VS800 and WATO EX-20 series vital signs monitors. It fits the connector and bay dimensions of the VS800 chassis and matches the voltage rail the BMS expects at handshake. Capacity is 6400mAh (71.04Wh) — sourced from product data, not estimated.
- VS800 and WATO EX-20 platform fit: These monitors share the same battery bay geometry, 11.1V nominal rail, and BMS communication protocol. One cell pack covers both platforms without adapter or modification.
- Bench tested on actual hardware: We cycled this pack through full charge and discharge on VS800 hardware. The BMS completed cell authentication, accepted the charge profile without fault flags, and held voltage within spec under the monitor's ECG and SpO2 simultaneous load.
- Post-swap self-test handling: After installing this battery, let the VS800 complete its full power-on self-test without interrupting it. The device runs a BMS verification sequence at startup — cutting power mid-sequence writes a battery fault to memory that persists until the next clean reboot.
VS800 low-battery alarm firing immediately after a confirmed full charge
The VS800's charge IC applies a conservative acceptance threshold when it first sees a new cell. If the internal cell voltage hasn't settled after initial charge, the BMS reads capacity below its alarm trigger — typically below 10.5V resting — and fires the alert even though the pack is physically full. This is a calibration gap, not a defective cell. Run one complete charge-discharge cycle through the monitor before treating any low-battery alarm as valid. After that cycle, the BMS learns the actual cell profile and alarm thresholds normalise.
VS800 failing to complete boot sequence after battery sat in storage
Li-ion cells self-discharge during storage. If the pack voltage drops below approximately 9V, the VS800's BMS enters deep-discharge protection and blocks normal startup — the device either shows a blank screen or halts mid-boot. Connect the monitor to AC mains power and leave it on charge for a minimum of four hours before attempting to boot on battery alone. Once the cell recovers above the BMS recovery threshold, the boot sequence completes normally.