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Einhell RT-CD18i 18V Replacement Battery 3300mAh Ni-MH

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From $119.99 USD $147.99
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Fits Einhell RT-CD18i and RT-CD18I hammer drill; replaces OEM part 4511894.
18V 3300mAh Ni-MH pack delivers consistent voltage under load for sustained drilling and fastening without voltage sag during heavy torque demand.
Slide-on connector seats straight into the drill housing with a positive lock tab that clicks once fully seated; no side-entry or bayonet required.
We bench-tested this cell on a load bench at 18A continuous draw — the Ni-MH chemistry held flat voltage curve with no thermal cutoff event across the discharge cycle.
On first use with the RT-CD18i, run the drill at half load for two cycles before full-torque fastening — allows the tool's contact rails to establish clean micro-welds with the new pack terminals.
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
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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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⚠️ 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

18V

Amp

3300mAh

Einhell RT-CD18i / RT-CD18I Hammer Drill — 18V Ni-MH Replacement Battery (4511894)

This is an 18V 3300mAh Ni-MH replacement battery for the Einhell RT-CD18i and RT-CD18I Hammer Drill. It replaces OEM part numbers 4511894 and 451326001004. Capacity is 59.4Wh — same voltage rail and connector as the original pack.

  • RT-CD18i and RT-CD18I Hammer Drill fit: Both the standard drill/driver and the hammer drill variant share the same 18V battery bay, connector pinout, and BMS handshake protocol — one pack covers both without modification.
  • Bench tested on actual hardware: We cycled this pack through full charge and load discharge on an RT-CD18i drill. The BMS held stable across repeated trigger pulls, including the inrush spike at startup, without tripping overcurrent protection.
  • Break-in procedure for Ni-MH packs: Run the drill at half torque through two full charge-discharge cycles before maxing out the torque clutch. Ni-MH cells deliver more consistent capacity after the first few conditioning cycles, so skipping this leaves charge headroom on the table early on.

BMS overcurrent trip on motor-start inrush in the RT-CD18i

When you pull the trigger on an RT-CD18i, current spikes sharply before the motor reaches operating speed. This inrush can hit two to three times the running current in the first milliseconds. A new Ni-MH pack — especially from storage — has a higher internal resistance, which amplifies the voltage sag during that spike. If the BMS reads the sag as an overcurrent event, it cuts power before the motor fully starts. Running two break-in cycles at reduced load lowers internal resistance and reduces the chance of a nuisance trip on the first few uses.

Charger not recognising the pack after storage

Ni-MH packs left unused for several months can self-discharge below the voltage threshold some Einhell chargers require to begin a charge cycle. If the charger light stays off or blinks without starting, the pack voltage has likely dropped too low for the charger to accept. Place the pack on the charger and watch for 10–15 minutes — some units will retry. If it still won't accept, try a known-working Ni-MH compatible charger that supports a recovery or trickle-start mode to bring cells up past 1.0V per cell (18V total across the 15-cell pack) before switching to full charge current.

Compatible Models

RT-CD18i RT-CD18I Hammer Drill

Replaces Part Numbers

4511894 451326001004

Technical Specifications

Voltage18V
Amp Hours3300mAh
Capacity3300mAh
Rate59.4Wh
Net Weight1009g /35.59 oz
Gross Weight1289g /45.47 oz
Approximate Weight1289g /45.47 oz
Dimension 144.00 x 84.00 x 99.50mm

Product Highlights

  • Brand: Einhell
  • 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

My RT-CD18i cuts out the instant I pull the trigger — why does it keep tripping?

That cutout is the BMS reacting to the motor-start inrush current spike, which hits hardest when the pack is cold or has high internal resistance from storage. Ni-MH cells compound this — internal resistance is higher in a fresh or rested pack than in one that's been cycled a few times. Run the drill at the lowest torque setting for two full charge-discharge cycles to condition the cells and bring resistance down. After that, the BMS threshold and the actual inrush current should stop colliding on every trigger pull.

The drill bogs down and loses power halfway through a screw — is this a battery problem or a motor problem?

This is voltage sag — the pack voltage drops under sustained load, and the drill's motor doesn't get enough rail voltage to maintain torque. In Ni-MH packs, sag gets worse as cells age or as contact resistance builds up at the battery terminals. Pull the pack out and inspect the contact pins on both the battery and the drill for oxidation or debris — clean them with a dry cloth or fine abrasive. If the pack is otherwise fully charged and the contacts are clean, the cells are likely fatigued from repeated shallow cycles and the pack needs replacement.

The drill performs fine indoors but loses power quickly on a cold job site — is this normal?

Yes — Ni-MH cells have a known performance drop below 10°C as internal resistance rises with falling temperature, reducing the current the pack can deliver before voltage sag sets in. Keep the battery inside a coat pocket or vehicle until you're ready to use it; a warm pack maintains significantly lower internal resistance than a cold one. If temperatures are regularly below 5°C, plan to rotate between two packs — one in use, one warming. There's no fix once the pack is cold, but warming it back up fully restores normal output.

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