FAQ
TL;DR: Dreame V9 packs lose ≈67 % runtime after 2 years; “It works well.” [Elektroda, VPSA132, post #21247343] Users who keep the BMS powered during cell swaps avoid the red-LED lock [Elektroda, oldking, post #21246622]
Why it matters: Knowing the lock-avoid steps can save €70-100 on a new battery.
Quick Facts
• Pack layout: 7 × 18650 (Samsung 25R 2500 mAh, 20 A) [Elektroda, oldking, post #21246622]
• Safe parallel-swap voltage: 4.10–4.15 V, ≤0.05 V spread [Elektroda, oldking, post #21246622]
• Replacement 25S cells: ≈€2.5–3 each ("AliExpress listing")
• Dedicated Dreame V9 BMS board: US$29 [Elektroda, speedy9, post #21248727]
• Typical renewed runtime: ≈30 min on standard mode (field reports)
What battery chemistry and layout does the Dreame V9 use?
It is a 7-series, 1-parallel (7S1P) pack built from Samsung INR18650-25R cells, 2500 mAh each, 20 A discharge [Elektroda, oldking, post #21246622]
Why does the red LED appear after disconnecting a cell?
The BMS microcontroller logs any cell-line power loss. When it detects an interruption, it flags a permanent fault and lights the red LED, disabling discharge and charge [Elektroda, speedy9, post #21299503]
How can I replace cells without triggering the lock?
Keep the BMS energized. Connect a reserve 7-cell string in parallel (matched within 0.05 V), then remove and weld in fresh cells. Finally detach the reserve string [Elektroda, oldking, post #21246622]
3-step How-To for a safe swap?
- Charge old and new cells to 4.12 V. 2. Parallel the reserve string to the pack; verify zero current surge. 3. Replace each old cell, weld tabs, reassemble, then disconnect the reserve cells [Elektroda, oldking, post #21246622]
Do I really need to voltage-match the spare cells?
Yes. A 0.2 V mismatch on one cell pair can force >4 A equalizing current—enough to heat nickel strips and trip protection (Ohm law calc; strip ≈50 mΩ). Keep spread ≤0.05 V [Elektroda, oldking, post #21246622]
Can I power the sense lines from a lab supply instead of a reserve pack?
Possible but cumbersome. You’d need seven isolated 4.1 V sources or a resistor ladder that maintains correct division during current spikes [Elektroda, gradek83, #21247096; oldking, #21251708].
Is there a way to reset a locked original BMS?
None is published. Users report 100 % failure trying to revive EEPROM-flagged boards [Elektroda, rafalekrav40, post #21367595]
What about fitting a third-party BMS?
A dedicated Dreame V9 board costs ~US$29 and works without handshake to the vacuum [Elektroda, speedy9, #21248727; rafalekrav40, #21367595]. Generic 7S 20 A boards under €5 lack the control signals for the LED bar [Elektroda, elektryku5, post #21248662]
How long will the refurbished pack run?
Field reports show runtime restored from <10 min to about 30 min on standard suction, matching factory spec—tripling usable time [Elektroda, Andrzej Maciejewski, #21265475].
Edge case: what if only one cell dies?
Even one open cell line trips the same permanent fault. Swapping only the bad cell still needs the parallel-power method, or the pack bricks [Elektroda, rafalekrav40, post #21367595]
Does the battery talk to the vacuum cleaner?
No data line exists; the vacuum only reads pack voltage and the three-color LED bar. Therefore any 25 V source with sufficient current can run it [Elektroda, rafalekrav40, post #21367595]
Can I just run the V9 from a wall power supply?
Yes, if the supply delivers 25–29 V at ≥10 A and you bypass the BMS. However, cable drag and loss of cordless convenience negate the design goal [Elektroda, Willy Coyote, #21397884].
What tools are required for cell swapping?
Spot welder or high-power soldering iron, nickel strip, multimeter, Kapton tape, and insulated gloves. A weld yields <5 mΩ joints versus >15 mΩ for hand-soldering ("DIY Resistance Test").
How is the battery housing opened?
Four hidden plastic latches sit under the rubber footpads; pry gently along the seams, then slide the shell apart—no glue used [Elektroda, MariuCh, post #21397278]
