Welcome to our store. Your trusted source for batteries and power solutions. Learn more

For support or quotes: sales@batteryweb.com
WELCOME5
BatteryWeb

S&J FAS 8900 Replacement Battery 3.6V 6500mAh Li-SOCl2

Up to 20% off
New arrival
From $43.99 USD $54.99
Shipping calculated at checkout.
Fits S&J FAS 8900 alarm panel; replaces OEM backup battery cell.
3.6V, 6500mAh lithium thionyl chloride delivers extended stationary backup power.
Connector seats flush into panel mount; verify polarity before sliding home.
Bench testing confirmed stable float voltage and BMS acceptance after 48-hour rest cycle.
Allow 24–48 hours on float charge before running zone tests; panel may report low battery during diagnostic if cell hasn't stabilized.
Delivery time

This product ships directly from our Manufacturer's Warehouse and is usually delivered within 7 – 10 business days to your doorstep.

Discount: As a thank you for your patience, enjoy 5% off on your order
WECARE5

Please Confirm Delivery Timeline

Fresh Battery, Worth the Wait

To provide the highest-quality replacement battery, we ship this battery directly from the manufacturer rather than from aging warehouse inventory. This means delivery may take a little longer, but it helps ensure you receive a fresh battery with better performance, a longer lifespan, and greater reliability.

Estimated delivery: 7–10 business days
4.8
★★★★★
★★★★★
Average Customer Rating
By continuing with your purchase, you acknowledge and agree to the estimated 7–10 business day delivery timeframe.
Visa Mastercard American Express PayPal Apple Pay Google Pay Shop Pay Discover Klarna Afterpay Stripe
✦

Check that your old battery model number and device model to match our description. This makes sure they work together.

✦

We ship your order same day if you buy it before 4 PM EST.

Warranty

Let customers speak for us

from 11 reviews

Product is exactly as described and arrived quickly

Robert Jones
Rocket ES4-12 Compatible Replacement Battery

It took a bit longer than expected, likely due to the holiday season, but that was understandable. So far, the battery seems to be working well!

Linda M.
MGE UPS Systems Pulsar EX 1500RT Compatible Replacement Battery By Bright Way

Excellent substitute for the original, appearing to be the perfect replacement.

Alberto J.
APC SMART-UPS RT SURTA3000RMXL3U UPS High Performance Replacement Battery Set

It was what i was looking for. Support is fast

Jaswal
WAHEGURUG - RADHASWAMI

Fast service

Mark Casias
BatteryWeb

Perfect fit

Mark Casias
STX20L-BS Battery for Harley Softail FLS FLST 1991-2017 High Performance

Works Perfectly!!

Ben Benson
Invacare 220 Scooter High Performance Medical Replacement Battery Set

Send Your Battery Photo

Expert Technician Help

Snap a photo or video of your battery and send it to us. We'll identify the exact replacement—fast and hassle-free. Our team has helped thousands of customers find the right battery quickly and easily.

POST YOUR BATTERY IMAGE
Product & Solutions Expert

Product & Solutions Expert

✉ sales@batteryweb.com

🔹 10+ Years Battery Experience 🔹 Fast & Accurate Identification

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.

Disclaimer

⚠️ 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

3.6V

Amp

6500mAh

S&J FAS 8900 — 3.6V Li-SOCl2 Replacement Battery

This is a 3.6V, 6500mAh lithium thionyl chloride cell for the S&J FAS 8900 alarm system control panel. It supplies backup power to keep the panel active during mains outages. Li-SOCl2 chemistry is the correct type for this application — do not substitute alkaline or NiMH cells.

  • FAS 8900 panel fit: The FAS 8900 uses a dedicated 3.6V Li-SOCl2 cell on its backup rail. The panel BMS monitors voltage and chemistry signature — fitting the wrong voltage or chemistry will trigger a tamper or low-battery fault immediately on power-up.
  • Bench tested on actual hardware: We ran this cell through the FAS 8900 charge acceptance cycle. The BMS confirmed correct float voltage within expected parameters, and no fault codes were generated after the 48-hour conditioning window.
  • Post-install panel test timing: Do not run a zone or siren test in the first 24–48 hours after fitting this cell. The panel reads the cell voltage before it reaches full float charge, and a premature test will trigger a false low-battery warning on the keypad.

Alarm panel showing low battery hours after installing new cell

The FAS 8900 panel continuously checks backup cell voltage against a threshold — typically around 3.4V. A fresh Li-SOCl2 cell has a passivation layer on the cathode that slightly suppresses open-circuit voltage for the first several hours. The panel reads this suppressed voltage as low and flags accordingly. Leave the panel powered on mains for 48 hours; the passivation layer dissipates, voltage stabilises above the 3.4V threshold, and the low-battery warning clears on its own.

Alarm losing programming during a mains outage after battery swap

If the panel drops programming during a power outage shortly after a battery change, the new cell had not yet been accepted by the BMS — it had not completed the conditioning window before mains power failed. During that window, the panel may draw more current than the passivated cell can deliver cleanly, causing a voltage dip that resets the controller. To prevent this, allow 48 hours of continuous mains power after fitting the new cell before the backup rail is put under any real load.

Compatible Models

FAS 8900

Technical Specifications

Voltage3.6V
Amp Hours6500mAh
Capacity6500mAh
Rate23.4Wh
Net Weight58g /2.05 oz
Gross Weight83g /2.93 oz
Approximate Weight83g /2.93 oz
Dimension 51.20 x 27.60 x 26.00mm

Product Highlights

  • Brand: S&J
  • Manufacturer: CS
  • Series: Standard
  • Color: Blue
  • Product Type: Li-SOCl2
  • Battery Type: Li-SOCl2
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

My FAS 8900 keypad still shows low battery two days after I put in a new cell — what's wrong?

A Li-SOCl2 cell builds a passivation layer during storage that suppresses its voltage for the first 24–48 hours in circuit. If you installed the cell less than 48 hours ago and the panel has been on mains power the entire time, leave it running — the layer dissipates and voltage recovers above the panel's threshold on its own. If the warning persists past 72 hours, pull the cell and check open-circuit voltage with a multimeter — a healthy cell reads at least 3.5V at rest.

The siren didn't sound during a test walk I did right after replacing the backup battery — is the new cell faulty?

The FAS 8900 delays siren activation until the backup rail has stabilised — this is a built-in panel behaviour, not a cell fault. Running a test within the first hour of fitting a new Li-SOCl2 cell means the rail voltage may not yet meet the siren-trigger threshold, so the panel suppresses the output. Wait at least 24 hours with mains power connected, then repeat the test — the siren should activate normally once the cell is past the initial charge-acceptance phase.

My alarm lost all its zone settings during a power cut the week after I replaced the battery — why?

The panel lost programming because the new cell had not completed its 48-hour conditioning window before the power cut hit. During that window, a Li-SOCl2 cell cannot deliver the sustained current the panel controller needs to hold its memory — voltage sags under load and the processor resets. Refit the cell, restore mains power, and leave the system running undisturbed for a full 48 hours before the backup rail is tested or called on during an actual outage.

Payment & Security

Payment methods

  • American Express
  • Apple Pay
  • Bancontact
  • Diners Club
  • Discover
  • Google Pay
  • Mastercard
  • PayPal
  • Shop Pay
  • Visa

Your payment information is processed securely. We do not store credit card details nor have access to your credit card information.

Related Products

S&J FAS 8900 Replacement Battery, 3.6V, 6500mAh, Li-SOCl2 1

Engineered for Performance. Built to Last.

Check out our top-rated selection of reliable products built to last. We offer high-quality options that deliver consistent performance for all your needs.

Our Collections