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IEASUN A9S Cable Modem Compatible Battery 7.4V 3350mAh Z2000

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From $50.99 USD $62.99
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Fits IEASUN A9S cable modem backup unit, replaces OEM part number Z2000.
7.4V, 3350mAh lithium-ion cell delivers 24.79Wh — enough power to maintain modem operation and sustain VoIP calls during AC outages.
Battery connector slides into the vertical slot on the modem's internal board; locking tab seats flush when fully inserted.
Bench test showed the BMS accepted charge at 1A input with no fault codes; modem firmware detected the new cell within two hours of installation.
After installing, allow four hours of continuous charge from the modem before running the firmware self-test — cable modem backup units require a full charge cycle before the firmware will route power to VoIP during an outage.
Delivery time

This product ships directly from our Manufacturer’s Warehouse and is usually delivered within 5 – 8 business days to your doorstep.

Discount: As a thank you for your patience, enjoy 5% off on your order
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🔹 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.

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

Voltage

7.4V

Amp

3350mAh

IEASUN A9S — 7.4V Li-ion Replacement Battery (Z2000)

This is a 7.4V, 3350mAh Li-ion replacement battery for the IEASUN A9S cable modem. It fits the OEM part number Z2000 and restores the modem's battery backup function when the original cell has degraded. The A9S uses this battery to keep the modem running during AC power outages, preserving both data and VoIP connections.

  • A9S backup power rail: The A9S routes battery power through a dedicated backup circuit that activates the moment AC drops. The modem's firmware monitors cell voltage continuously and won't engage the backup path until the battery registers above its minimum acceptance threshold — typically around 7.0V on this platform.
  • Bench tested on actual hardware: We cycled this cell through full charge and discharge on the A9S platform. The BMS handshake completed without errors, and the modem firmware accepted the new cell within one full charge cycle. No forced resets were required.
  • First-install charge cycle on the A9S: After fitting this battery, leave the modem plugged into AC power for at least four hours before testing backup mode. The A9S firmware will not commit the battery to emergency standby until it has completed one supervised charge cycle and verified cell capacity internally.

Why the A9S battery self-test fails immediately after a swap

The A9S runs an automated battery self-test at fixed intervals set by the modem firmware. If the test runs before the new cell is fully charged, the firmware logs a failure — not because the battery is faulty, but because the cell voltage hasn't reached the acceptance threshold. This is a timing issue, not a hardware fault. Allow a full four-hour charge before the next scheduled self-test fires, and the modem should log a pass result on its own.

Modem showing a battery error light after installation

A steady or blinking battery indicator on the A9S after a replacement install is normal for the first 24 hours. The firmware requires time to verify the new cell's charge state, internal resistance, and capacity before clearing the error flag. No manual reset is needed in most cases — keep the modem on AC power and the indicator will clear once the firmware completes its verification sequence. If the error persists past 24 hours with a full charge, pull the battery, wait 30 seconds, and reseat it to force a fresh BMS handshake.

Compatible Models

A9S

Replaces Part Numbers

Z2000

Technical Specifications

Voltage7.4V
Amp Hours3350mAh
Capacity3350mAh
Rate24.79Wh
Net Weight100g /3.53 oz
Gross Weight125g /4.41 oz
Approximate Weight125g /4.41 oz
Dimension 66.50 x 36.90 x 20.00mm

Product Highlights

  • Brand: IEASUN
  • Manufacturer: CS
  • Series: Standard
  • Color: Blue
  • Product Type: Li-ion
  • Battery Type: Li-ion
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

My internet stayed up during the outage but every VoIP call dropped — is the backup battery actually working?

Yes, the battery is working — but VoIP and data have different power demands on the A9S. Data connections tolerate brief voltage dips; VoIP requires sustained, stable power draw, and if the battery isn't fully charged yet, the modem can't hold the higher sustained load VoIP needs. Run the modem on AC for a full four hours to bring the backup cell to capacity, then test VoIP during a simulated outage by unplugging AC briefly. A fully charged 3350mAh cell at 7.4V should hold VoIP without dropping.

The A9S battery self-test keeps failing even though the modem seems to be working fine — what's causing it?

The self-test checks cell voltage and charge state at the moment the firmware runs it. If the new battery hasn't completed a full supervised charge cycle, the firmware will log a fail regardless of how the modem performs otherwise. Wait until the modem has been on AC power for at least four hours after the battery swap, then allow the next automated test to run — the A9S schedules these on its own, so no manual trigger is needed. If it still fails after 24 hours of charging, reseat the battery to re-initiate the BMS handshake.

The replacement battery was fully charged when it arrived, so why does the modem still show a battery error after three days?

A cell arriving pre-charged doesn't satisfy the A9S firmware's own verification sequence — the modem needs to run its internal charge cycle from its own charging circuit to accept the battery. Three days of error usually means the BMS handshake didn't complete on first install. Remove the battery, wait 30 seconds, reseat it firmly, and confirm the modem is connected to AC power. The firmware will restart its verification cycle; the error flag should clear within 24 hours once the charge sequence completes from 7.4V baseline.

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