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Fakir Robert II 14.4V Replacement Battery 31 21 140

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From $54.99 USD $67.99
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Fits Fakir Robert II and RS 710 cordless vacuums; replaces OEM part 31 21 140.
14.4V lithium-ion at 2600mAh delivers stable voltage to the motor under full suction load.
Connector seats flush into the battery dock with a single locking tab; orientation is keyed.
Bench testing showed clean BMS handshake on first insertion; no cutoff or throttling observed under sustained motor draw.
Do not leave this cell on the charging dock continuously — trickle charging degrades capacity faster than charge-to-full and removal cycles.
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Battery Care Tips

🔹 Getting Started

Charge your new battery fully before you use it for the first time. Over the next few charge cycles, run your device down to around 20% before you recharge—this helps the battery perform its best. After that, charge whenever you need to.

🔹 Keep It Healthy

Avoid letting your battery completely drain or staying plugged in constantly. Both extremes wear it out faster. Store the battery in a cool, dry place when you're not using it, since heat damages batteries quickly.

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🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.

Voltage

14.4V

Amp

2600mAh

Fakir Robert II / RS 710 — 14.4V Li-ion Replacement Battery (31 21 140)

This is a 14.4V, 2600mAh Li-ion replacement battery for the Fakir Robert II and RS 710 cordless vacuum cleaners. It replaces OEM part number 31 21 140. Fit the battery, click it into the dock, and the vacuum runs as it did with the original cell.

  • Robert II and RS 710 compatibility: Both models run the same 14.4V platform with the same battery bay geometry and BMS handshake. One cell fits both — no adapter, no modification needed.
  • Bench tested on actual hardware: We cycled this cell through charge and discharge on the RS 710 platform. The BMS communicated correctly with the charger, held the voltage rail steady under full suction load, and tripped at the correct low-voltage cutoff without triggering a fault state.
  • Dock charging on the Robert II: Do not leave this vacuum sitting on the charging dock continuously. Cordless vacuums on permanent dock charge develop capacity fade faster than units charged only when depleted. Charge to full, then remove from the dock.

Suction dropping before the battery indicator reaches low

The Robert II motor draws harder when airflow is restricted — a partially blocked filter forces the motor to pull more current than its rated draw. That sustained overcurrent causes voltage sag on the battery rail, which the BMS reads as a low-cell condition and throttles power before the indicator registers empty. Clean or replace the filter first. If suction recovers and holds, the battery is not the cause.

Motor cutting out mid-run and then recovering after a short pause

This is a BMS overcurrent trip, not a dead battery. When the motor is working against a sustained blockage or a fully clogged filter, current spikes above the BMS threshold and the cell disconnects to protect itself. After 30–60 seconds the BMS resets, and power returns. Clear the blockage, check the filter, and run the vacuum again. If it cuts out again on an unblocked floor, measure cell voltage — a degraded cell will sag below 12V under load and trigger the same trip.

Compatible Models

Robert II RS 710

Replaces Part Numbers

31 21 140

Technical Specifications

Voltage14.4V
Amp Hours2600mAh
Capacity2600mAh
Rate37.44Wh
Net Weight240g /8.47 oz
Gross Weight420g /14.82 oz
Approximate Weight420g /14.82 oz
Dimension 106.75 x 58.36 x 43.20mm

Product Highlights

  • Brand: Fakir
  • Manufacturer: CS
  • Series: Standard
  • Color: Black
  • Product Type: Li-ion
  • Battery Type: Li-ion
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

My Fakir Robert II battery drains noticeably faster than it did when new — the filter is clean, so what else causes this?

Continuous dock charging is the most common cause of capacity fade on these vacuums. Keeping the battery on the dock after it reaches full charge exposes the cells to a constant low-level trickle that accelerates degradation over weeks. Remove the battery or the unit from the dock once charging is complete. A replacement cell showing this same fade quickly is almost always the result of going straight back onto permanent dock charge.

The Robert II motor cuts out after a few seconds on carpet, then restarts — is this a battery fault or something else?

That cut-and-recover pattern is a BMS overcurrent trip triggered by sustained high motor draw, not a dead cell. Thick carpet increases motor resistance; if the filter is even partially restricted at the same time, current spikes past the BMS protection threshold and the cell disconnects. Clear the filter completely, then test on carpet again. If the trip still happens, check cell voltage at rest — a healthy 14.4V cell should read between 15.8V and 16.8V fully charged.

The replacement battery (31 21 140) won't charge on the Robert II dock — charger light stays on but the cell never gets warm or shows charge progress.

The Robert II charger expects a specific BMS handshake before it begins the charge cycle. If the charger light stays static and the cell stays cold, the BMS has not responded to the handshake signal — this usually means the cell arrived deeply discharged below the charger's detection threshold. Remove the battery, wait two minutes, refit it firmly, and try again. If the dock still shows no charge activity after a second attempt, verify the battery contacts are clean and fully seated; oxidised contacts break the data line the BMS uses to initiate the charge handshake.

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