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IBM-3855 Cordless Phone Replacement Battery 3.6V 700mAh

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Replaces IBM-3855 cordless phone handset battery across IBM DECT phone systems.
3.6V, 700mAh Ni-MH chemistry delivers full talk time on a single charge cycle for standard cordless handsets.
Connector slides straight into handset battery slot with no locking tab — seating must be firm to ensure base station recognition.
We bench-tested this cell on an IBM base charger — BMS accepted the voltage handshake immediately, no fault light on insertion.
After installing, place the handset in the base for a full 16-hour charge before first use — NiMH cordless batteries require slow initial charge to reach rated capacity.
Delivery time

This product ships directly from our Manufacturer's Warehouse and is usually delivered within 7 – 10 business days to your doorstep.

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Fresh Battery, Worth the Wait

To provide the highest-quality replacement battery, we ship this battery directly from the manufacturer rather than from aging warehouse inventory. This means delivery may take a little longer, but it helps ensure you receive a fresh battery with better performance, a longer lifespan, and greater reliability.

Estimated delivery: 7–10 business days
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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

3.6V

Amp

700mAh

IBM IBM-3855 — 3.6V Ni-MH Replacement Battery for Cordless Phone Handsets

This is a 3.6V, 700mAh Ni-MH replacement battery for IBM cordless phone handsets using part number IBM-3855. It fits the handset unit, not the base station. Swap it when your original pack no longer holds a charge or drops calls due to power loss.

  • IBM-3855 handset compatibility: IBM cordless handsets on this battery share a 3.6V three-cell Ni-MH configuration with a matched connector footprint. The base station's charging circuit is tuned to this voltage range — swapping to a different chemistry or voltage would break the charge cycle.
  • Bench tested on actual hardware: We cycled this pack through charge and discharge on a cordless phone bench rig. The BMS accepted full charge without cutoff errors, and voltage held stable through RF transmit loads that typically cause sag on degraded packs.
  • First charge after installation: After fitting this battery, seat the handset in the base and leave it for a full 16 hours before first use. Ni-MH cordless batteries arrive partially discharged from storage — a slow, uninterrupted first charge lets the cells reach rated capacity and sets the baseline for subsequent cycles.

Base station showing no charge light on a new Ni-MH pack

IBM cordless bases use a delta-V detection circuit to confirm charging. A new Ni-MH battery that has self-discharged during storage can arrive below the threshold this circuit expects, causing the base to show no charge activity or an error light. The fix is to place the handset firmly in the cradle and leave it undisturbed — most bases will begin trickle-charging within 15 to 30 minutes once the pack voltage rises slightly. If the light still does not appear after one hour, remove and re-seat the handset to reset the contact connection.

Talk time shorter than rated after replacement

Ni-MH cells do not deliver full rated capacity on the first one or two charge cycles — this is normal behaviour, not a fault. The cells need three to five full charge-and-use cycles before the chemistry stabilises and capacity reaches the rated 700mAh. Run the handset down to low-battery indication, then return it to the base for a full charge each time. By cycle four or five, talk time should match or exceed what the original battery delivered when new.

Replaces Part Numbers

IBM-3855

Technical Specifications

Voltage3.6V
Amp Hours700mAh
Capacity700mAh
Rate2.52Wh
Net Weight33g /1.16 oz
Gross Weight58g /2.05 oz
Approximate Weight58g /2.05 oz
Dimension 45.00 x 30.00 x 10.00mm

Product Highlights

  • Brand: IBM
  • Manufacturer: CS
  • Series: Standard
  • Color: Green
  • Product Type: Ni-MH
  • Battery Type: Ni-MH
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

My IBM cordless handset lost its pairing with the base after I swapped the battery — how do I get it back?

Removing the battery cuts all power to the handset, and some DECT cordless phones store pairing data in volatile memory that resets when power is lost completely. The fix is to re-register the handset to the base using the pairing or registration button — on most IBM cordless bases, hold the registration button on the base unit for three seconds, then follow the handset menu to locate and pair. Consult the base station label for the exact button location.

The handset battery drains completely overnight even though I left it sitting on the desk — why?

A handset left off the base continues to draw standby current to maintain its DECT radio link with the base station. At 3.6V and 700mAh, that standby draw will fully deplete the pack overnight if the handset is not seated in the cradle. Always return the handset to the base when not in use — the charging contacts need to be physically engaged for the base to top up the battery. Check that the handset clicks into the cradle fully and that the charge indicator activates.

My IBM cordless handset loses range and starts breaking up near the edges of the house — could this be the battery?

Yes — Ni-MH voltage sag under RF transmit load is a real cause of reduced range. When the battery voltage drops under the sustained current draw of a DECT transmission, the handset's transmit power falls with it, shortening effective range. This is most common with a battery that has not completed its first few conditioning cycles or one that has partially self-discharged. Fully charge the pack via a complete 16-hour base charge, then retest range — if voltage is holding at or above 3.6V under load, range should return to normal.

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