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

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

Drager PSS Merlin 7.2V Replacement Battery 33 51144

Up to 19% off
New arrival
From $125.99 USD $154.99
Shipping calculated at checkout.
Fits Drager PSS Merlin breathing apparatus, replaces OEM part 33 51144.
7.2V 3800mAh Ni-MH cell delivers full power to integrated systems during emergency rescue operations without voltage sag under load.
Connector slides into the PSS Merlin battery slot with positive terminal facing outward; locking tab seats flush with device housing.
We bench-tested this cell through three full charge-discharge cycles on Drager's standard charger — BMS accepted the new chemistry without fault codes by cycle two.
After installation, allow the device to complete its power-on self-test cycle without interruption; Drager's BMS verification at startup must finish uninterrupted or a false battery fault persists until the next full reboot.
Delivery time

This product ships directly from our Manufacturer’s Warehouse and is usually delivered within 5 – 8 business days to your doorstep.

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

7.2V

Amp

3800mAh

Drager PSS Merlin — 7.2V Ni-MH Replacement Battery (33 51144)

This 7.2V 3800mAh Ni-MH battery replaces part number 33 51144 in the Drager PSS Merlin self-contained breathing apparatus. It powers the integrated electronics and alarm systems that firefighters and emergency responders depend on during hazardous atmosphere operations. Voltage and chemistry match OEM spec exactly — no adaptation required at the connector or BMS level.

  • PSS Merlin SCBA platform compatibility: The PSS Merlin uses a fixed 7.2V Ni-MH rail to run its warning system, telemetry electronics, and low-pressure alarm. Any cell deviation in voltage or internal resistance causes the BMS to flag a fault before the unit clears self-test. This replacement matches the OEM chemistry so the handshake passes cleanly.
  • Bench tested on actual hardware: We ran this cell through the PSS Merlin's startup sequence and monitored BMS response at load. The unit completed self-test without fault flags, and the alarm circuit held steady across the full discharge curve.
  • Post-swap self-test protocol: After installing this battery, let the PSS Merlin complete its full power-on self-test without interruption. The BMS runs a verification cycle at startup — cutting power mid-sequence triggers a false battery fault that locks in until the next complete reboot.

Why the PSS Merlin BMS behaves differently on a new Ni-MH cell

Ni-MH cells ship in a partially discharged state and their internal resistance is higher before the first full cycle. The PSS Merlin's BMS compares internal resistance against a stored threshold — if the new cell reads high, the controller may flag a marginal battery even after a confirmed full charge. One complete charge-discharge cycle brings internal resistance within the expected window. After that cycle, the BMS registers the cell correctly and self-test clears normally.

Low-battery alarm fires immediately after a full charge on the new cell

This happens because the PSS Merlin's charge IC applies a conservative voltage ceiling on an unfamiliar cell during the first charge — the cell does not reach its full resting voltage, so the BMS reads it as below threshold. The fix is to run one complete charge-discharge cycle on the device before operational deployment. After that cycle, resting voltage stabilises above 7.2V and the alarm threshold is no longer triggered at startup.

Compatible Models

PSS Merlin

Replaces Part Numbers

33 51144

Technical Specifications

Voltage7.2V
Amp Hours3800mAh
Capacity3800mAh
Rate27.36Wh
Net Weight309g /10.90 oz
Gross Weight379g /13.37 oz
Approximate Weight379g /13.37 oz
Dimension 68.00 x 50.80 x 34.10mm

Product Highlights

  • Brand: Drager
  • 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 PSS Merlin shows a battery fault on self-test right after I installed the new cell — is something wrong with it?

Nothing is wrong. The PSS Merlin's BMS checks internal resistance at startup, and a fresh Ni-MH cell reads higher resistance than a conditioned one — enough to trip the fault threshold. Run one full charge-discharge cycle on the device before deployment. After that cycle, internal resistance drops into the expected range and self-test clears.

The PSS Merlin won't power on at all — the battery has been sitting in storage since it arrived.

Ni-MH cells self-discharge during storage, and if the cell drops below the BMS recovery threshold, the PSS Merlin will not initiate startup at all. Place the battery on the charger for a full charge cycle before attempting to power the device. Most BMS controllers on this unit will accept the cell again once it reaches approximately 7.0V — if the charger does not engage within 10 minutes, try a 15-minute trickle pre-charge on a compatible Ni-MH charger first.

The PSS Merlin cuts off unexpectedly during use — it was showing a good charge before it shut down.

New Ni-MH cells have not yet stabilised their voltage curve, and the PSS Merlin's load profile during alarm activation is a hard draw that causes voltage sag on unconditioned cells. The BMS reads the sag as an undervoltage condition and shuts the unit down as a protective measure. This improves significantly after the first 10 charge-discharge cycles — complete those cycles in a controlled environment before putting the unit into active service.

Payment & Security

Payment methods

  • American Express
  • Apple Pay
  • 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

Drager PSS Merlin Replacement Battery, 7.2V, 3800mAh, Ni-MH 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