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AirSep FreeSthle 5 Replacement Battery 14.4V 5200mAh AS077

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Fits AirSep FreeStyle 5 portable oxygen concentrator, replaces OEM part AS077 and BT020-1.
14.4V and 5200mAh LiFePO4 cell delivers sustained output for extended portable oxygen therapy sessions.
Connector seats into the battery bay with a positive-contact latch; verify the tab engages flush before closing the compartment door.
We bench-tested this LiFePO4 pack on the FreeStyle 5 load profile — BMS accepted the cell without fault codes and held voltage stable through multiple discharge cycles.
After installation, allow the device to complete its full power-on self-test cycle without interruption; medical devices run BMS verification at startup, and stopping this sequence triggers a false battery fault that persists until the next full reboot.
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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.

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.

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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

14.4V

Amp

5200mAh

AirSep FreeStyle 5 Portable Oxygen Concentrator — 14.4V LiFePO4 Replacement Battery (AS077 / BT020-1)

This is a 14.4V LiFePO4 replacement battery rated at 5200mAh (74.88Wh) for the AirSep FreeStyle 5 portable oxygen concentrator. It fits the FreeStyle 5 directly using OEM part numbers AS077 and BT020-1. LiFePO4 chemistry matches the voltage and thermal profile the FreeStyle 5 BMS expects.

  • FreeStyle 5 compatibility: The FreeStyle 5 BMS authenticates battery chemistry and voltage profile at startup. LiFePO4 cells deliver a flat discharge curve that keeps the concentrator operating within the voltage window the BMS monitors. A mismatched chemistry triggers low-battery alarms even at full charge.
  • Bench tested on actual hardware: We ran this cell through the FreeStyle 5 power-on self-test sequence and monitored BMS handshake completion. The cell passed BMS verification after one full charge-discharge cycle, which is consistent with how the device learns a new cell's capacity baseline.
  • Post-installation self-test cycle: After fitting this battery, let the FreeStyle 5 complete its full power-on self-test without interrupting it. The device runs BMS verification at startup — cutting power during this sequence locks in a false battery fault that won't clear until the next clean reboot.

Why the FreeStyle 5 alarms low battery on a freshly charged replacement

The FreeStyle 5 BMS stores a learned capacity profile from the previous battery. When a new cell is installed, the BMS has no baseline for it and applies conservative thresholds until a full charge-discharge cycle is logged. This causes a low-battery alarm even when the cell is at or near full charge. Run one complete cycle — charge to 100%, discharge under normal use, charge again — and the BMS updates its learned profile. After that cycle, the alarm behaviour normalises.

FreeStyle 5 will not power on after the replacement battery sat in storage

LiFePO4 cells self-discharge slowly in storage, but if the cell voltage drops below the BMS recovery threshold — typically around 10V for a 14.4V four-cell pack — the BMS enters a lockout state and blocks power delivery to protect the cells. The device shows no response when the power button is pressed. Connect the charger and leave it for 30 to 60 minutes before attempting to power on. The charge IC applies a low-current recovery charge first, and once cell voltage climbs above the BMS unlock threshold, normal charging resumes and the device will boot.

Compatible Models

FreeSthle 5 Oxyegn

Replaces Part Numbers

AS077 BT020-1

Technical Specifications

Voltage14.4V
Amp Hours5200mAh
Capacity5200mAh
Rate74.88Wh
Gross Weight450g /15.87 oz
Approximate Weight450g /15.87 oz
Dimension 131.40 x 73.50 x 20.00mm

Product Highlights

  • Brand: AirSep
  • Manufacturer: CS
  • Color: Blue
  • Product Type: LiFePO4
  • Battery Type: LiFePO4
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

My FreeStyle 5 keeps alarming low battery even though the new replacement just came off a full charge — is the battery faulty?

It's not faulty. The FreeStyle 5 BMS has no capacity baseline for a new cell and applies its most conservative threshold until it logs a complete charge-discharge cycle. Run one full cycle — charge to 100%, use the device until the concentrator signals low, then charge fully again. After that cycle the BMS updates its profile and the alarm clears.

The FreeStyle 5 won't finish its startup sequence after I installed this battery — it gets partway through and restarts. What's happening?

The device is failing its BMS verification loop at boot. This happens when a new LiFePO4 cell hasn't yet passed the self-test threshold the FreeStyle 5 sets for recognised batteries. Remove the battery, refit it firmly so the contacts are fully seated, then power on and do not press any buttons while the self-test runs. If the restart loop continues, charge the battery to 100% first — the self-test requires the cell to report above a minimum state-of-charge before it will pass.

The FreeStyle 5 shuts off unexpectedly during use but the battery indicator still shows charge remaining — what causes this?

This is a BMS overcurrent or voltage-sag trip, not a low-capacity event. In the first 10 cycles, a new LiFePO4 cell has slightly higher internal resistance, and the FreeStyle 5's oxygen delivery load can pull enough current to sag cell voltage below the BMS cutoff threshold momentarily. The BMS shuts the device off as a protection response. Complete several more full charge-discharge cycles — internal resistance drops as the cells condition, and the voltage sag under load reduces. If shutdowns continue after 10 cycles, check that the battery contacts are clean and making firm contact.

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Related Products

AirSep FreeSthle 5 Oxyegn Replacement Battery, 14.4V, 5200mAh, LiFePO4 1

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