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

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

TETRA Cassidian THR9 BLN-5i Replacement Battery 3.7V 2300mAh

Up to 19% off
New arrival
From $42.99 USD $52.99
Shipping calculated at checkout.
Fits Cassidian THR9 and HT9588AA two-way radio; replaces BLN-5i, BLN-6, BLN-Ex-2 U batteries.
3.7V at 2300mAh delivers full RF output power across the shift without mid-transmission cutoff.
Connector plugs straight into the battery slot with no locking tab — seats flush when fully inserted.
We bench-tested this pack with sustained PTT cycles; BMS held voltage under transmit current spikes without shutdown.
On first charge with the THR9 dock, if the fault LED stays lit after insertion, remove the battery, wipe the gold contact strip with a dry cloth, and reseat firmly — the radio platform needs a clean contact cycle to accept the new BMS handshake before charging begins.
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

3.7V

Amp

2300mAh

TETRA Cassidian THR9 / HT9588AA — 3.7V Li-ion Replacement Battery (BLN-5i)

This is a 3.7V, 2300mAh Li-ion replacement battery for the Cassidian THR9 TETRA portable radio and compatible variants including the HT9588AA and HR8509AA. It replaces OEM part numbers BLN-5i, BLN-6, and BLN-Ex-2 U. The THR9 is a professional digital radio used in public safety, security, and commercial communications environments.

  • THR9 / HT9588AA / HR8509AA platform fit: These three models share the same battery bay geometry, contact layout, and BMS handshake protocol. A single cell pack with the correct 3.7V rail and BLN-5i form factor fits all three without modification.
  • Bench tested on actual hardware: We cycled this pack through full charge and discharge passes on the THR9 platform. The BMS accepted charge current without fault, held voltage through simulated PTT transmit load spikes, and released to the charger dock cleanly on each cycle.
  • First insertion into charger dock: If the dock shows a fault LED on first insertion, remove the pack, wipe the gold contact strip with a dry cloth, and reseat firmly. The THR9 dock requires a clean contact cycle to register the new BMS before charging begins.

Why the THR9 cuts out mid-transmission on a new BLN-5i pack

The THR9 draws a sharp current spike the moment PTT is pressed — RF output, speaker drive, and digital baseband all load the cell simultaneously. A new pack shipped at storage voltage (typically around 3.6V) sits close to the BMS undervoltage threshold before any real discharge has occurred. That spike can momentarily pull the cell below the cutoff, triggering a BMS trip and killing the transmission. Run one full charge cycle before putting the radio into active service — this brings the cell to 4.2V and gives the BMS adequate headroom to absorb the PTT transient.

Bar indicator showing one fewer bar than expected after fitting this pack

The THR9 uses a voltage-threshold bar indicator — each bar corresponds to a voltage band, not a fuel gauge reading. A new cell at storage voltage reads in the lower bands immediately after insertion, which looks like a low or degraded battery. This is not a fault with the pack. Place it on charge until the dock shows a full charge indication, then reinsert — the indicator will reflect the correct voltage and display the expected bar count.

Compatible Models

CASSIDIAN THR9 HT9588AA HR8509AA

Replaces Part Numbers

BLN-5i BLN-6 BLN-Ex-2 U

Technical Specifications

Voltage3.7V
Amp Hours2300mAh
Capacity2300mAh
Rate8.51Wh
Net Weight67g /2.36 oz
Gross Weight117g /4.13 oz
Approximate Weight117g /4.13 oz
Dimension 97.46 x 53.62 x 14.96mm

Product Highlights

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

Frequently Asked Questions

My THR9 cuts out exactly when I press PTT — is this a faulty battery or the radio?

This is the BMS tripping on the transmit current spike, not a faulty radio. When PTT is pressed, the THR9 pulls a sharp load surge that can drop a storage-voltage cell below the BMS cutoff threshold for a split second. Charge the pack fully to 4.2V before first use — that gives the BMS the voltage headroom it needs to absorb the PTT transient without tripping.

The THR9 drops to low TX power partway through a shift even though the battery showed full at the start — what's happening?

This is voltage sag under sustained RF output, not a capacity fault. As the cell discharges under continuous or frequent transmit load, the voltage drops into the range where the THR9 reduces output power to protect the radio and the pack. The radio is behaving as intended. If this happens earlier in the shift than expected, check that the dock reached a full charge indication — a partial charge will push the sag point earlier in the cycle.

The charger dock fault LED came on after I inserted the new pack and it never cleared — how do I fix it?

The dock is rejecting the BMS handshake, usually because the gold contacts didn't make clean contact on insertion. Remove the pack, wipe the contact strip on both the battery and the dock with a dry cloth, and reseat the pack with firm, even pressure until it clicks. If the fault LED persists, the cell may have dropped below the dock's acceptance voltage threshold during shipping — place the pack in a known-good THR9 radio for 30 seconds to allow the BMS to initialise, then transfer it to the charger.

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

Airbus THR9 Replacement Battery, 3.7V, 2300mAh, Li-ion 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