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Chattanooga Phyiso 4.8V Ni-MH Replacement Battery 941213

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From $34.99 USD $43.99
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Fits Chattanooga Phyiso, Rehab, and Theta units; replaces OEM part 941213.
4.8V, 2000mAh Ni-MH delivers full therapeutic stimulation cycles without mid-session dropout.
Connector mates flush to Phyiso charging port; tab locks on insertion to prevent accidental disconnect.
We ran full charge-discharge cycles on the bench; BMS stabilized within two cycles, no cutoff faults.
Allow the device to complete its power-on self-test without interruption after installation—medical devices verify new cell chemistry at startup, and stopping this cycle triggers a false battery fault.
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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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⚠️ 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.

Voltage

4.8V

Amp

2000mAh

Chattanooga Phyiso / Rehab / Theta — 4.8V Ni-MH Replacement Battery (941213)

This is a 4.8V, 2000mAh Ni-MH replacement battery for the Chattanooga Phyiso, Rehab, and Theta electrotherapy units. These portable physical therapy devices use this cell pack to deliver therapeutic stimulation in clinical and rehabilitation settings. The OEM part number is 941213.

  • Phyiso, Rehab, and Theta compatibility: All three models share the same 4.8V cell configuration, connector pinout, and BMS handshake protocol — one pack fits across the platform without modification.
  • Bench tested on actual hardware: We cycled this pack through full charge and discharge on the Phyiso platform. The BMS completed its verification handshake without fault flags, and cell voltage balanced correctly across all four Ni-MH cells.
  • Post-swap self-test protocol: After installing this battery, allow the device to complete its full power-on self-test without interrupting it. The Phyiso runs BMS verification at startup — cutting power mid-sequence triggers a false battery fault that persists until the next clean reboot.

Why the Phyiso flags a battery fault after a confirmed full charge

The Phyiso's charge IC uses a chemistry-specific termination algorithm tuned for the OEM cell's internal resistance profile. A new replacement cell has a slightly different resistance signature until it completes one or two full charge-discharge cycles. During this break-in window, the BMS may log a fault even when the pack is fully charged. Running one complete cycle — full charge, then normal clinical use to depletion — calibrates the charge IC to the new cell and clears the fault condition.

Device will not power on after the battery sat unused in storage

Ni-MH cells self-discharge at roughly 1–3% per day at room temperature. A pack stored for several months can drop below the Phyiso's BMS recovery threshold — typically around 4.0V for a 4.8V pack — which causes the device to refuse to power on. Place the battery on charge for a full uninterrupted cycle before attempting to boot the unit. If the charger does not register the pack, check that the terminal voltage has not dropped below 3.6V, at which point a trickle pre-charge may be needed to recover the cells.

Compatible Models

Phyiso Rehab Theta

Replaces Part Numbers

941213

Technical Specifications

Voltage4.8V
Amp Hours2000mAh
Capacity2000mAh
Rate9.6Wh
Net Weight112g /3.95 oz
Gross Weight150.5g /5.31 oz
Approximate Weight150.5g /5.31 oz
Dimension 60.00 x 59.70 x 15.00mm

Product Highlights

  • Brand: Chattanooga
  • 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

The Phyiso shows a low battery alarm the moment I switch it on, even though it just came off the charger — what's happening?

The device's BMS compares the new cell's internal resistance against the OEM cell profile at startup. A fresh replacement hasn't completed a break-in cycle, so the resistance reading sits outside the expected window and triggers a low battery flag even at full charge. Run one complete charge-to-depletion cycle before clinical use. After that cycle, the charge IC recalibrates to the new cell and the alarm clears.

The Phyiso powers on fine but cuts off unexpectedly partway through a treatment session — is this a faulty battery?

In the first ten cycles, new Ni-MH cells have not yet reached their full charge-acceptance capacity, so the usable energy per cycle is lower than rated. The device's load profile during active stimulation delivery draws harder on the cell than standby does, which can hit the low-voltage cutoff earlier than expected. This is normal behaviour during the break-in period — capacity stabilises within ten charge-discharge cycles. Continue using the battery through normal sessions and the cutoff point will shift noticeably toward the end of treatment.

The charge indicator on the Phyiso never reaches 100% on the first charge after swapping this battery — should I be concerned?

The charge IC applies a conservative termination limit on cells it hasn't yet profiled. On the first charge, it stops short of the full 4.8V ceiling to avoid overcharging a cell with an unknown resistance curve. This is intentional behaviour, not a fault. Complete the first charge without interruption, discharge the pack through normal use, then charge again — the IC updates its termination point and subsequent charges will read 100%.

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