The 21V 2A Li-Ion charger that knows when to stop — reliable protection for your 18V batteries
Do you need to charge your 18V power tool battery without worrying about overcharging? This 2A charger efficiently powers up your 18650 cell packs, with an internal circuit that automatically cuts off power the moment the voltage hits 21V. You can leave your workshop with complete peace of mind, knowing your batteries are safe.
Note: Before use, please ensure your battery has a nominal voltage of 18V, is a Li-Ion 5S configuration, and features a 2.1 × 5.5 mm DC jack. This charger is not compatible with NiMH, NiCd batteries, or proprietary branded battery packs (e.g., Bosch, Makita, etc.).
Why choose this model? (Key Benefits):
- Automatic 21V cut-off — The protection circuit stops the current exactly when the pack is full, eliminating the risk of overcharging even if left plugged in for extended periods.
- Compatible with any 5S BMS pack — Perfect for aftermarket power tool batteries, DIY 18650 cell packs, and any other 5S configuration with a standard 2.1 × 5.5 mm DC jack.
- Extra-long 250 cm cable — Reach wall sockets easily without needing an extension lead, ideal for busy workshops where your workbench is far from the power source.
- Universal 100–240V AC input — Use it across Europe and beyond without needing an additional voltage adapter.
- Clear LED indicator — Instantly see the status of your charge cycle without having to dismantle anything.
- Compact design: 135 × 55 × 35 mm — Fits easily into any toolbox and won’t clutter your shelf space.
Performance and Specifications
The internal switched-mode power supply accepts inputs between 100 and 240V AC, making it fully compatible with standard 230V mains power. The output is stabilized at exactly 21V DC — the precise requirement for a 5S Li-Ion pack (5 cells in series, each charged to a maximum of 4.2V). The 2A current provides an optimal balance between charging speed and thermal stress on your 18650 cells.
The 2.1 × 5.5 mm DC connector (standard barrel jack) is the most common interface for aftermarket batteries and custom-built packs. Once the 21V threshold is reached, the integrated protection circuit automatically interrupts the current, ensuring no extra voltage is applied to the cells regardless of how long the charger remains connected.
| Feature | Specification |
|---|---|
| Input Voltage | 100–240V AC |
| Frequency | 50–60 Hz |
| Compatible Battery Nominal Voltage | 18V Li-Ion |
| Output Voltage (Charging) | 21V DC |
| Output Current | 2A |
| Compatible Cell Configuration | 5S (5S BMS), 18650 cells |
| Output Connector | 2.1 × 5.5 mm DC (barrel jack) |
| Cable Length | 250 cm |
| Dimensions | 135 × 55 × 35 mm |
| Status Indicator | LED |
| Protection | Overcharge (auto-shutoff at 21V) |
Package Contents
- 1× 21V 2A Li-Ion Charger with 2.1 × 5.5 mm DC plug, 250 cm cable
Frequently Asked Questions
Does this work with standard 18V power tool batteries?
It is compatible with aftermarket 18V Li-Ion batteries that use a 2.1 × 5.5 mm DC jack. It is not compatible with original branded batteries (e.g., Bosch, Makita, DeWalt), as these use proprietary connectors that do not fit a standard barrel jack.
What is a 5S BMS and why does it matter?
It means your battery pack consists of 5 Li-Ion cells connected in series. Each cell charges to a maximum of 4.2V, so 5 × 4.2V = 21V — exactly what this charger provides. The BMS (Battery Management System) inside your pack protects the cells from overcharging, over-discharging, and short circuits.
Can I use this for DIY batteries made from 18650 cells?
Yes, it is ideal for custom-built 5S packs used in DIY tools, portable systems, or small electric vehicles. The only requirement is that your pack must have a 5S BMS and a 2.1 × 5.5 mm DC jack.
How long does a full charge take?
It depends on your battery capacity. A 4Ah pack will charge in approximately 2 hours at 2A (4Ah ÷ 2A = 2h), plus a few extra minutes for the final voltage balancing phase.
What does the LED indicate once the battery is full?
The LED will change colour or remain steadily lit to signal that the charging cycle is complete and the current has been automatically cut off. Exact LED behaviour may vary slightly between production batches.
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