Toys & light bricks
LEGO Light Brick battery
2 × 1.5V alkaline button cell
A LEGO light brick uses two LR41 alkaline button cells. LEGO’s Demon Bull King (80010) product page states 2× LR41 for the light brick; Bricks and Lights (11009) also names LR41. Remove the underside screw, replace both cells matching orientation, and keep button cells away from children.
How to replace it
| How to open | On the underside of the light brick, remove the small cross-head screw and separate the base. Note cell orientation, remove both old LR41 cells, insert two fresh LR41/AG3 cells the same way round, then reseat the base and screw. New bricks may have a black pull-tab — remove before first use. The brick typically lights only while the switch is pressed. |
|---|---|
| Orientation | Match the orientation of the factory cells — do not reverse polarity |
| Access | tool_assisted |
| Notes | Use a well-fitting precision Phillips screwdriver; tiny bits can strip the screw. Replace both cells together — do not mix old and new. |
Important
- Button cells are a choking / swallowing hazard — keep new and used LR41 cells away from children; secure the compartment fully after replacement.
- Some LEGO set marketing lines undercount pack contents (e.g. “an LR41” for a set). Per-brick power is two LR41 cells on official 80010 copy and common light-brick construction.
- SR41 is the silver-oxide size twin — LEGO specifies LR41 alkaline button cells.
Sources
Helpful for this device
Optional tools for opening, testing or charging — separate from the battery answer.
- Fluke 101 Digital Multimeter
Accurate open-circuit voltage and basic electrical checks
- Klein Tools MM400 Multimeter
General DC voltage checks including battery terminals
- Digital multimeter
Measure open-circuit voltage and general electronics checks
New battery but still not working?
A fresh 2 × LR41 should restore LEGO Light Brick (2×3 LED) if the battery was the problem. Work through the checks below before replacing the device.
- Check orientation
Confirm the cell is seated correctly: Match the orientation of the factory cells — do not reverse polarity
- Check the battery type
This device needs 2 × LR41 (alkaline). Rechargeable cells are not supported for this device. Same size does not always mean the same battery.
- Check known model-specific issues
Button cells are a choking / swallowing hazard — keep new and used LR41 cells away from children; secure the compartment fully after replacement. Some LEGO set marketing lines undercount pack contents (e.g. “an LR41” for a set). Per-brick power is two LR41 cells on official 80010 copy and common light-brick construction. SR41 is the silver-oxide size twin — LEGO specifies LR41 alkaline button cells.
- Confirm the battery itself
For most coin cells, fitting a known-good fresh cell of the correct code is simpler than capacity testing.
- Still not responding?
If a correct, fresh battery installed properly does not restore the device, the fault may be elsewhere — the device may need service or replacement.
Replacing the device?
LEGO Light Brick (2×3 LED) is still sold new. Only consider a replacement if the checks above did not help.
Need to replace the device?
LEGO Light Brick (2×3 LED) is still sold new. Only buy another if a fresh battery and the checks above did not help.