T-Mobile 3BN78319 Octopus Open Cordless Phone Replacement Battery 3.6V 700mAh
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T-Mobile 3BN78319 Octopus Open Cordless Phone Replacement Battery 3.6V 700mAh - is backordered and will ship as soon as it is back in stock.
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Battery Care Tips
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
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
⚠️ 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.
T-Mobile 3BN78319 Octopus Open Cordless Phone Replacement Battery 3.6V 700mAh - is backordered and will ship as soon as it is back in stock.
Voltage
3.6V
Amp
700mAh
T-Mobile Octopus Open / Octophon Open 400 D — 3.6V Ni-MH Replacement Battery (3BN78319)
This 3.6V, 700mAh Ni-MH pack replaces the original battery in the T-Mobile Octopus Open and Octophon Open 400 D cordless handsets. It matches the OEM voltage, capacity, and connector spec for a direct swap. Dimensions are 51.09 × 36.94 × 11.11mm — confirm fitment against your existing cell before installing.
- Octopus Open and Octophon Open 400 D compatibility: Both handsets run the same 3.6V NiMH cell with identical connector and physical format. OEM references 3BN78319, 3BN66305AAAA041030, 3BN66305AAAA000904, and ALCH-011644AC all cross to this pack.
- Bench tested on actual hardware: We cycled this pack through charge and discharge on a DECT handset rig. The BMS accepted standard base-station charge current without interruption and voltage held stable across the RF transmit window.
- First-charge protocol for NiMH cordless packs: After installing, seat the handset in the base and leave it there for a full 16 hours before first use. NiMH cells shipped from storage need a slow, uninterrupted charge to reach rated capacity — a short first charge locks in reduced capacity from the start.
Why the Octopus Open shows shorter talk time after a battery swap
NiMH cells don't deliver full rated capacity on the first cycle out of storage. The chemistry needs three to five full charge-discharge cycles before the cell reaches 700mAh. Running the handset until it cuts off and then charging fully in the base each time accelerates this break-in. Expect rated performance by cycle four or five.
Base station charge light stays off or shows an error after fitting the new pack
NiMH cells in storage drop below the voltage threshold that some DECT base stations require before accepting a charge. The base reads the resting voltage as a fault rather than a depleted cell. To recover, remove the battery, leave it at room temperature for 30 minutes, then reseat the handset firmly in the cradle. If the base still doesn't respond, check the cradle contacts are clean — oxidised contacts on 3.6V circuits cause the same symptom.
Compatible Models
Replaces Part Numbers
Technical Specifications
Product Highlights
- Brand: T-Mobile
- Manufacturer: CS
- Series: Standard
- Color: Black
- Product Type: Ni-MH
- Battery Type: Ni-MH
- Warranty: 12 Months
- Bulk Orders: sales@batteryweb.com
Frequently Asked Questions
My Octopus Open handset stopped pairing with the base after I swapped the battery — did I break something?
No — some DECT handsets lose their pairing record when power is fully removed during a battery swap. The fix is a fresh registration: hold the handset's pairing button and trigger the base-station registration sequence as described in the handset manual. Re-pairing takes under two minutes and restores full function.
Talk time is noticeably shorter than my original battery for the first few days — is the new cell faulty?
Not faulty — this is normal NiMH behaviour after storage. Cells arrive partially discharged, and the chemistry needs three to five full cycles before it reaches rated 700mAh capacity. Run the handset until it cuts off, then charge uninterrupted in the base for 16 hours each time. Capacity climbs steadily across those cycles.
The handset loses range near the edges of my home after fitting the new pack — the old battery never did this.
Range drops when NiMH voltage sags under the RF transmit load — a cell that hasn't completed break-in can't sustain the voltage the DECT radio needs at full power. This resolves as the pack conditions over the first few cycles. If range is still reduced after five full cycles, check the cell is seated firmly and the contacts are making clean metal-to-metal contact.
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