About this replacement
Deerma DEM-NU05 / NU05 — 7.4V Li-ion Replacement Battery (INR18650-2S1P)
This is a 7.4V 2600mAh Li-ion replacement battery for the Deerma DEM-NU05 and NU05 cordless vacuum cleaner. It uses two 18650 cells wired in a 2S1P configuration, matching the voltage rail and connector of the original pack. Capacity is 2600mAh (19.24Wh) — taken from the product specification, not estimated.
- DEM-NU05 and NU05 compatibility: Both model designations share the same battery bay, connector pin-out, and BMS handshake protocol. The INR18650-2S1P part number covers both variants — the hardware is identical across the two naming conventions Deerma uses in different markets.
- Bench tested on actual hardware: We cycled this pack through multiple charge and discharge runs on the DEM-NU05 platform. The BMS engaged cell balancing correctly at the top of charge, and low-voltage cutoff triggered cleanly without requiring a manual reset.
- Contact condition before charging: The DEM-NU05 is used close to floors and furniture where dust and fine debris collect quickly. Wipe the battery contacts and the dock pins with a dry cloth before seating the battery — debris bridging the contacts causes the BMS to register a fault and block charging entirely.
Why the DEM-NU05 loses suction power before the battery indicator drops
The vacuum's motor draws a short current spike each time suction load increases — picking up heavier debris or switching to a denser surface. An aged or weakened cell pack cannot hold voltage steady through these spikes, so the BMS throttles output to protect the cells. The indicator light reads the resting cell voltage, not the loaded voltage, so it can show partial charge while the motor is already starved. Replacing the cell pack restores the voltage headroom the motor needs to sustain full suction under load.
Battery seated correctly but the charging LED won't come on
This is usually a BMS protection lock triggered by a deeply discharged cell, not a dock or adapter fault. When a Li-ion cell drops below approximately 2.5V per cell, the BMS opens the charge circuit as a safety measure and will not accept a standard charge signal. Remove the battery, leave it out for two minutes, then reseat it firmly — this clears the BMS latch on some packs and allows a recovery charge to begin. If the LED still does not respond, check dock voltage at the pins; it should read between 8.0V and 8.4V DC.