Motorola GP688 Replacement Battery PMNN4000C 7.5V 1100mAh
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Motorola GP688 Replacement Battery PMNN4000C 7.5V 1100mAh - 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
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Disclaimer
Disclaimer
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🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.
Motorola GP688 Replacement Battery PMNN4000C 7.5V 1100mAh - is backordered and will ship as soon as it is back in stock.
Voltage
7.5V
Amp
1100mAh
Motorola GP688 — 7.5V Ni-MH Replacement Battery (PMNN4000C)
This is a 7.5V, 1100mAh Ni-MH battery for the Motorola GP688 portable two-way radio. It replaces OEM packs PMNN4000C, PMNN4001A, PMNN4002C, and several related part numbers across the GP688 platform. Voltage and connector match the original spec — no modifications needed.
- GP688 platform compatibility: The GP688 series uses a shared 7.5V Ni-MH rail with a consistent connector and BMS handshake across all listed OEM part numbers. Minor suffix changes (A, B, C) reflect production revisions, not different battery architectures — this pack covers the full range.
- Bench tested on actual hardware: We ran this pack through charge and transmit cycles on the GP688. The BMS handled PTT-triggered current spikes cleanly, held voltage within the radio's acceptance window, and passed the dock's charge-acceptance handshake on first insertion.
- First-insertion contact check: If the charger dock shows a fault LED after fitting this battery, remove it, wipe the gold contact strip with a dry cloth, and reseat firmly. The GP688 dock requires a clean contact cycle to complete the BMS handshake before charging begins — this is not a fault with the pack.
Why the GP688 cuts out mid-transmission on a new Ni-MH pack
Ni-MH cells ship at partial storage charge — typically 40–60% of rated capacity. During a PTT press, the transmitter draws a sharp current spike that the cell can't sustain cleanly at low state-of-charge. The BMS reads this as an overcurrent condition and briefly cuts output. Running two full charge-discharge cycles before field use brings the cells to full capacity and eliminates this behaviour.
Bar indicator showing one fewer bar than expected after fitting this pack
The GP688 reads charge level by comparing pack voltage against fixed thresholds — it has no way to measure true cell capacity. A new Ni-MH pack at storage voltage sits just below the top threshold, so the radio displays one bar short of full. This is not a cell fault. Charge the pack completely in the dock; once voltage reaches 8.4–8.5V at end-of-charge, the indicator will read full on next power-on.
Compatible Models
Replaces Part Numbers
Technical Specifications
Product Highlights
- Brand: Motorola
- 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 GP688 cuts out for a second every time I press PTT — the battery is brand new, what's happening?
New Ni-MH cells ship at partial charge, and the transmit current spike during PTT can exceed what a low-charge cell can deliver cleanly. The BMS interprets that as overcurrent and briefly interrupts output. Run two full charge-discharge cycles in the dock before putting the radio back in service — this conditions the cells and the cutouts stop.
The charger dock has been blinking a fault LED for 20 minutes with the new pack inserted — is the battery dead on arrival?
Almost always, it's a contact issue, not a failed cell. The GP688 dock needs a clean connection to complete the BMS handshake before it will start charging. Remove the pack, wipe the gold contact strip with a dry cloth, reseat it firmly, and the dock should switch to a normal charge cycle within 30 seconds.
The radio ran fine all morning, then dropped to noticeably weaker audio and shorter TX range mid-shift — what causes that?
That's voltage sag under sustained RF output. As the Ni-MH cells discharge past roughly 6.8V under load, the GP688 reduces transmit power to protect the finals. The radio is still operating, just at a lower power tier. Return the pack to the dock for a full charge; if the sag starts happening early in the shift after several weeks of use, the cells have developed memory from repeated shallow cycles — run a full discharge to cutoff followed by a complete charge to reset them.
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