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NEC G266 Compatible Battery 3.7V 1200mAh Li-ion

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From $22.99 USD $28.99
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Fits NEC G266, G277, and G355 cordless handsets; replaces original 3.7V lithium-ion battery pack.
3.7V and 1200mAh capacity delivers full talk and standby time matching OEM performance on DECT base stations.
Connector slides straight into handset battery slot with positive terminal facing the spring contact; no adapter needed.
We bench tested the CS-AY4020CL against a discharged original pack — BMS accepted base station charge without fault codes on first insertion.
After installing, seat the handset in the base for a full 16-hour charge cycle before regular use; Li-ion cells in DECT phones require steady initial charging to reach rated capacity.
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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.

Delivery and Shipping

🔹 Most orders ship the next day, and we use FedEx, UPS, Purolator and other carriers to get them to you. Lithium batteries have to ship by ground only, not air or USPS. Make sure your address is right before you order, because if we have to send it back, you pay for shipping again.

Disclaimer

⚠️ Disclaimer: All product names, trademarks, and registered trademarks belong to their respective owners.

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

Voltage

3.7V

Amp

1200mAh

NEC G266 / G277 / G355 Series — 3.7V Li-ion Replacement Battery

This 3.7V, 1200mAh Li-ion battery fits NEC cordless handsets across the G266, G277, G277 DECT, and G355 series, plus additional compatible models. It replaces the original cell when the handset no longer holds a useful charge between base charges. Dimensions are 53.20 × 34.00 × 5.70mm — confirm against your existing battery before installing.

  • G-series handset compatibility: These NEC models share the same 3.7V Li-ion cell format, connector pinout, and physical footprint. One battery covers the full range without modification.
  • Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench. The BMS held charge termination correctly and showed no false-full cutoff at low state-of-charge after storage.
  • First charge after installation: Place the handset in the base and leave it for a full uninterrupted charge cycle before using it. Li-ion cells shipped in partial state-of-charge benefit from one complete charge before the first call.

Talk time shorter than expected after fitting this battery

A Li-ion cell shipped at storage charge — around 3.6–3.7V — hasn't been through a full cycle yet. The handset's fuel gauge or charge circuit may underestimate actual capacity until one complete charge-discharge cycle runs. After the first full charge from flat, rated capacity becomes available. If talk time stays short after three cycles, check that the handset is fully seated in the base cradle and the charging contacts are clean.

Handset loses pairing with base after battery replacement

Some NEC DECT handsets store pairing data in volatile memory that resets when power is fully removed during a battery swap. The handset wakes up after the swap as an unregistered unit. Re-register it through the base station menu — on most G-series models this is done by holding the FIND/PAGE button on the base for 3–4 seconds until the handset enters registration mode. Once paired, the handset operates normally.

Compatible Models

G266 G277 G277 DECT Handset G355 G566 G577 G955 GX266 GX566

Replaces Part Numbers

CE-MB206-5C-01 Q24-FR000000113082

Technical Specifications

Voltage3.7V
Amp Hours1200mAh
Capacity1200mAh
Rate4.44Wh
Net Weight23g /0.81 oz
Gross Weight48g /1.69 oz
Approximate Weight48g /1.69 oz
Dimension 53.20 x 34.00 x 5.70mm

Product Highlights

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

Frequently Asked Questions

My NEC G266 handset shows full charge on the base but goes dead after just a few minutes of use — what's wrong?

A cell that sat in storage at low voltage can trigger a false-full reading on the first charge because the base terminates early once it sees voltage climb quickly. Put the handset back in the base immediately after it goes flat and run a full uninterrupted charge. One complete charge from flat to full clears the false-full pattern and the handset will draw the rated 1200mAh from the next cycle onward.

The base station charge light stays orange or flashes an error after I installed the new battery — how do I fix it?

Li-ion cells shipped in partial state-of-charge sometimes come in below the voltage threshold the base expects before it starts a standard charge cycle. Remove the handset, wait 10 seconds, then reseat it firmly so the charging contacts align. If the error persists, check that the three contacts on the handset base are free of oxidation — clean them with a dry cloth and reseat again. The base should accept the cell and show a normal charge light within 60 seconds.

My NEC G355 handset drains completely overnight even when it's sitting in the base — is the battery faulty?

Overnight drain in the base is almost always a seating issue, not a cell fault. If the handset isn't fully clicked into the cradle, the charging contacts break intermittently and the standby draw runs off battery rather than mains. Reseat the handset until you feel or hear it click into position, then confirm the charge indicator lights up. If the light stays on and the handset still drains overnight, check for debris or corrosion on the cradle contacts and clean with a dry cloth.

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