IEASUN A9S Cable Modem Replacement Battery 7.4V 2600mAh Z2000

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

This is a 7.4V, 2600mAh Li-ion replacement battery for the IEASUN A9S cable modem. It slots into the modem's backup battery bay and provides power during outages so your connection stays live. Capacity is matched to the original Z2000 specification.

• A9S modem compatibility: The A9S uses a dedicated backup battery bay with a 7.4V two-cell Li-ion pack. The modem's BMS handshake checks cell voltage at insertion — this pack meets that threshold and registers correctly without firmware errors under normal conditions.
• Bench tested on actual hardware: We cycled this cell through the A9S charge controller. The BMS accepted the pack within the first charge cycle, held the correct float voltage, and the modem's battery indicator cleared without manual reset.
• First-use charge cycle on the A9S: After installing, leave the modem plugged into mains power for at least 4 hours before testing backup mode. The A9S firmware will not commit the battery to emergency power use until it completes one full supervised charge cycle from the modem's own charge controller.

Modem battery error after installation — what the firmware is actually doing

When a new cell is inserted, the A9S runs a battery acceptance sequence that can take up to 24 hours. During this window the modem may flag a battery error or show an amber battery LED — this is the firmware verifying cell chemistry, not a faulty battery. The charge controller needs to complete at least one full charge pass before the modem clears the fault. Do not pull and re-insert the battery during this period; that resets the acceptance timer. If the error persists beyond 24 hours of continuous mains power, check that the pack voltage reads at least 7.0V at the terminals.

Internet stays up during outage but VoIP calls drop immediately

Data and VoIP draw different sustained loads from the backup battery. The A9S allocates higher sustained current to voice channels, so a partially charged battery may support data traffic but cut VoIP the moment call signalling spikes current draw. This happens most often when the battery has not completed its initial 4-hour charge cycle. Fully charge the battery on mains power, then re-test by unplugging the modem and dialling out — the battery voltage under VoIP load should not drop below 6.8V for the call to hold.