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NEC i755 Cordless Phone Compatible Battery 3.7V 650mAh

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From $38.99 USD $47.99
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Fits NEC i755, i755d, i755S cordless phone handsets; replaces OEM part 690109.
3.7V Li-ion, 650mAh capacity delivers full talk time and standby runtime on the handset between base charges.
Connector slides onto the battery terminal contacts inside the handset; no locking tab — friction fit only.
We bench-tested this cell in a stock i755 base charger; BMS accepted voltage immediately, no fault light triggered.
After installing, place the handset in the base for a full 16-hour charge before first use — Li-ion packs in DECT phones need a slow ramp to allow the base station to calibrate charge detection properly.
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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.

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⚠️ 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

650mAh

NEC i755 Series — 3.7V Li-ion Replacement Battery (690109)

This is a 3.7V Li-ion battery rated at 650mAh (2.41Wh), built to the same spec as the original NEC part number 690109. It fits the NEC i755, i755d, and i755S cordless handsets. Install it when the original pack no longer holds charge or the handset dies well before you end a call.

  • i755 / i755d / i755S fit: These three handsets share the same battery bay dimensions, connector pinout, and 3.7V Li-ion cell requirement. One pack covers the whole family — no adapters or rewiring needed.
  • Bench tested on actual hardware: We cycled this pack through charge and discharge on the bench and verified the BMS held cutoff voltage correctly at both ends — no under-voltage sag that would trigger the handset's low-battery alert prematurely.
  • First charge after install: Place the handset in the base and leave it seated for a full charge cycle before making calls. Li-ion cells shipped in storage state need one complete charge to calibrate the handset's fuel gauge — skipping this often makes the battery meter read inaccurately for the first week.

Why the i755 handset shows low battery sooner than expected after a swap

The i755 reads remaining capacity by tracking voltage curves across a full charge cycle. A new Li-ion cell shipped in partial storage state has a compressed voltage profile until it completes its first full cycle. The handset's gauge interprets this compressed curve as low capacity and triggers the warning early — even though the cell itself is fine. After one full charge from flat to full, the voltage curve normalises and the indicator tracks correctly.

Handset not pairing with base station after battery replacement

Some DECT phones lose their handset-to-base pairing record when power is fully removed during a battery swap. The handset and base both store pairing keys in volatile memory, and a hard power loss can wipe the handset side. If the handset shows "searching" or "unregistered" after install, press and hold the Find/Page button on the base for 5–10 seconds to re-enter registration mode, then re-register the handset through its menu. This does not require a factory reset of the base.

Compatible Models

i755 i755d i755S 690111 SV8100 SL1100

Replaces Part Numbers

690109

Technical Specifications

Voltage3.7V
Amp Hours650mAh
Capacity650mAh
Rate2.41Wh
Net Weight36g /1.27 oz
Gross Weight71g /2.50 oz
Approximate Weight71g /2.50 oz
Dimension 79.46 x 45.24 x 10.30mm

Product Highlights

  • Brand: NEC
  • 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 i755 talk time is much shorter with the new battery than it was with the old one — is the replacement faulty?

A new Li-ion cell needs at least one full charge-discharge cycle before the handset's fuel gauge reads accurately. Until that cycle completes, the handset underestimates remaining capacity and shuts down early even though charge is still present. Run the handset from full to flat and then charge it uninterrupted to 100% — most units stabilise within two to three cycles. If talk time is still noticeably short after three cycles, check that the cell voltage at full charge reaches 4.2V.

The base station charge light stays red or shows an error after I put the handset in — what's wrong?

Li-ion cells shipped from storage can sit at a voltage the base station's charger circuit reads as "too low to accept." The base expects to see the cell above a minimum threshold — typically around 3.0V — before it starts the charge sequence. If the light stays red, remove the handset, leave it out for 30 seconds, then reseat it firmly. If the error persists, check that the battery contacts on the handset and base are clean and making full contact — a partial connection mimics a dead-cell error.

The handset drains overnight even when it's sitting in the base — is that the battery or the charger?

Overnight drain while docked points to the handset not making proper contact with the base charging pins, not a battery fault. When the connection is intermittent, the handset runs on battery in standby instead of drawing from the base. Remove the battery, clean the gold charging contacts on both the handset and base with a dry cloth, reinstall the battery, and reseat the handset so it clicks fully into the cradle. Confirm the base power LED is on before leaving it overnight.

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