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Sena SF2 Replacement Battery 3.7V 800mAh AHB802540

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From $30.99 USD $38.99
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Fits Sena SF2 and SF4 wireless headsets; replaces OEM part number AHB802540.
3.7V, 800mAh Li-Polymer cell delivers enough current for simultaneous audio playback and DECT radio transmission without voltage sag.
Connector seats into the SF2's battery slot with a single locking tab on the left side; orientation is keyed.
We bench-tested this cell in the SF2 base station — BMS accepted the handshake on first insertion, no fault codes, charging curve normal.
On first use, charge the headset in the base station for a full cycle before taking calls; DECT headsets require the base to log the new cell before talk-time estimates become accurate.
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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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🔹 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

3.7V

Amp

800mAh

Sena SF2 / SF4 — 3.7V Li-Polymer Replacement Battery (AHB802540)

This is a 3.7V, 800mAh Li-Polymer cell built to the AHB802540 specification. It fits the Sena SF2 and SF4 Bluetooth motorcycle helmet headsets. Swap it when the original cell no longer holds a charge or the headset shuts down mid-ride.

  • SF2 and SF4 compatibility: Both models share the same battery bay, connector pinout, and BMS handshake protocol. One cell covers both headsets without any hardware modification.
  • Bench tested on actual hardware: We cycled this cell through the SF2 charging circuit and monitored BMS communication. The protection circuit engaged correctly at low-voltage cutoff and the base station reported a full charge state after a complete cycle.
  • First charge after installation: Place the headset in the base station and let it run a complete charge cycle before pairing or taking a call. The SF2 base needs to complete this cycle to calibrate its talk-time indicator — skipping it causes the display to misreport remaining charge from the first use.

Why the SF2 cuts out mid-call even with a new battery installed

The SF2 draws current from two loads simultaneously — the audio amplifier and the Bluetooth radio. Under combined load, a cell sitting at storage voltage can sag below the BMS cutoff threshold briefly, triggering a shutdown. This is not a faulty cell. Run two or three full charge-discharge cycles through normal use and the resting voltage stabilises above the cutoff point. If drop-outs continue after three cycles, check the connector seating — the SF2 bay is shallow and a partially seated cell creates resistance that worsens voltage sag.

Base station shows charging error after fitting a replacement cell

The SF2 base station performs a BMS handshake at the start of every charge session. A new cell shipped at storage voltage (typically 3.6–3.7V) can cause the base to flag an error before the handshake completes. Remove the headset from the base, wait ten seconds, and reseat it firmly. If the error persists, connect the base to power first, then place the headset — this sequence lets the base initialise its charge controller before attempting communication with the new cell.

Compatible Models

SF2 SF4

Replaces Part Numbers

AHB802540

Technical Specifications

Voltage3.7V
Amp Hours800mAh
Capacity800mAh
Rate2.96Wh
Net Weight16g /0.56 oz
Gross Weight41g /1.45 oz
Approximate Weight41g /1.45 oz
Dimension 42.80 x 24.80 x 7.80mm

Product Highlights

  • Brand: Sena
  • Manufacturer: CS
  • Series: Standard
  • Color: Black
  • Product Type: Li-Polymer
  • Battery Type: Li-Polymer
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

My Sena SF2 talks for a few minutes then goes silent — the base showed a full charge before I left

A cell at storage voltage reads as "full" on the base indicator before it has been properly cycled. Under the combined draw of the Bluetooth radio and audio amplifier, that storage-voltage cell sags and hits the BMS cutoff fast. Run a complete charge cycle in the base station — power on, charge to green, then use the headset until it shuts off on its own — and repeat this two more times. By the third cycle the resting voltage stabilises and the early shutdowns stop.

Talk time is noticeably shorter on the new battery than it was when the original was new

Li-Polymer cells ship partially discharged and need three to five full charge-discharge cycles before they reach rated capacity. The SF2's 800mAh cell is no different — expect noticeably shorter use on cycles one and two. Run the headset down to automatic shutdown, charge fully in the base, and repeat. Capacity increases measurably with each cycle and levels out around cycle four or five.

The headset gets warm near the battery compartment during long rides — is that normal?

The SF2 housing is compact, and sustained dual-load draw — Bluetooth radio and audio running together — generates heat in a small space. Mild warmth at the battery compartment during extended use is within normal operating range for this cell size. If the headset becomes hot to the touch or shuts down due to heat, check that the battery compartment cover is fully closed — a gap traps heat against the cell instead of letting it dissipate. Operating above 40°C ambient (direct sun on a dark helmet) will accelerate this; store the headset out of direct sunlight between rides.

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