3S2P 18650 Battery Box – Bicycle Spotlight & Portable Power

Description

Compact. Rechargeable. Portable.

This handheld battery enclosure was designed as a power source for a bicycle spotlight. It houses six 18650 cells in a 3S2P configuration, a 3S BMS protection board, and a 3S USB charging module. Can be used to power any 12vdc device.

The front panel has a battery indicator and a three-position selector rocker. In my build, the rocker selects the spotlight’s orange LEDs or white LED, with the centre position providing off.

A GX16-4 output connector and USB-C charging port are accessible on one short end. Four M3 screws and threaded inserts secure the removable lid.

Features

• Compact enclosure that fits in your hand

• Designed around a six-cell 3S2P battery pack

• Front battery voltage and charge-level indicator

• Selector rocker for the two spotlight modes

• USB-C access for the 3S charging module

• GX16 output connection

• Two-part body and lid with M3 threaded fixings

• Adaptable to other compatible portable power projects

Battery configuration and capacity

3S2P means three groups connected in series, with two cells connected in parallel in each group.

With 3 Ah cells, each parallel pair provides 6 Ah, giving the complete pack a nominal capacity of 6 Ah / 6000 mAh.

Cell capacity varies between models. Actual capacity and runtime depend on the cells, their condition, the load, and operating conditions.

Output voltage changes with the battery’s state of charge. Use a spotlight or other load that accepts the pack’s full operating voltage range.

Included files

The download contains the enclosure models. Cells, electronic modules, connectors, wiring, and fasteners are separate components.

Hardware required

Alternative configurations

A two-terminal on/off rocker can be used for a simple switched output, provided it fits the opening and suits the circuit.

GX16 two-pin or three-pin versions may also be used where their mounting dimensions and contact arrangement suit the project. Check the mating connector and pin assignments when changing connector types.

Fit and compatibility

Check your components against the actual enclosure before printing:

• Indicator opening: 46 × 26.3 mm

• Rocker opening: 12.5 mm wide × 19.1 mm high

• GX16 opening: 16 mm diameter

• USB-C access opening: approximately 9.4 × 3.2 mm

Also check the battery arrangement, BMS size, charging-module position, component depth, and wiring clearance.

Suggested print settings

These are starting points rather than a tested print profile:

• Material: PLA

• Layer height: 0.20 mm

• Walls: 3–4 perimeters

• Infill: 100%

• Main body: Flat base on the build plate, open side facing up

• Lid: Exterior face on the build plate, internal locating features facing up

• Supports: Inspect the slicer preview around the connector openings

Assembly

1. Print both parts and clean up the openings.

2. Install the four M3 × 6 mm threaded inserts in the main body.

3. Fit the battery indicator, selector rocker, GX16 connector, and charging module.

4. Assemble and insulate the matched-cell 3S2P pack, following the instructions for the chosen BMS and charger.

5. Secure the pack and modules, and route wiring clear of the lid, screw posts, and component edges.

6. Verify polarity, connector pin assignments, charging operation, and both spotlight modes.

7. Secure the lid with the four M3 × 10 mm screws.

Provide suitable attachment and weather protection when using the completed box on a bicycle.

About this design

I designed this battery box to provide compact, rechargeable power for my bicycle spotlight while keeping the indicator, mode selection, charging, and output connections accessible. This is not limited to this function it can be used to power any 12vdc device.

If you print one, I’d love to see how you use it!

Designed by TD Circuits.

Happy printing!