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Battery

18650 Li-ion Battery Holder

Single-cell 18650 holder for portable project power.

A basic single-cell 18650 battery holder, the standard building block for portable and battery-powered maker projects. It's simply a molded plastic clip with spring-loaded metal contacts sized for the common 18650 cylindrical Li-ion cell, giving a solderable or wire-lead connection point without needing to solder directly onto the battery itself — which is important, since soldering onto an 18650's bare terminals can damage the cell and is generally discouraged.

Specifications

Cell compatibilitySingle 18650 Li-ion cell (18mm diameter x 65mm length)
Contact typeSpring-loaded positive and negative metal contacts, no direct soldering to the cell required
OutputRaw, unregulated battery voltage — typically 3.0V-4.2V depending on charge state
ConnectionBare wire leads (usually red/black) or PCB-mount pins, depending on holder style
MountingSurface-mount screw holes or PCB-through-hole pins, model-dependent
ProtectionNone built in — holder is purely mechanical; use a protected 18650 cell or add a separate protection/charge circuit (e.g. TP4056) for safe charging and discharge cutoff

Pinout

PinNameDescription
1+ (Positive lead)Connects to the cell's positive terminal via the spring contact
2- (Negative lead)Connects to the cell's negative terminal via the spring contact

The holder itself provides no charge control or over-discharge protection — pair it with a charge/protection module like the TP4056 (with built-in DW01 protection) if the project charges the cell in place, and always observe correct polarity since 18650 cells can vent or be damaged if reverse-connected.

Variants

Use the wire-lead version for quick breadboard prototyping and the PCB-mount version when designing a permanent custom board. Step up to a multi-cell holder only if the project genuinely needs more voltage (series) or runtime (parallel) than a single 18650 provides.

VariantTemp rangeHum rangeAccuracyProtocolPrice
Single-cell 18650 holder (wire leads)~$0.50-1
Single-cell 18650 holder (PCB mount)~$0.50-1.50
2-cell or 4-cell 18650 holder~$1-3

Board Integration

Wiring

Component pinBoard pinNote
+ (Positive lead)R1 (100k) to A0, R1 also to +Divider midpoint feeds A0 — keeps max voltage under 5V
+ (Positive lead)R2 (100k) from A0 to GNDSecond half of the divider — halves the battery voltage before it reaches A0
- (Negative lead)GNDCommon ground

Code

C++

Notes

A single 18650 cell is 3.0-4.2V, well under the Uno's 5V ADC reference, so a simple 1:1 (equal-value resistor) divider is enough headroom. Do not feed the raw cell voltage into VIN to power the Uno directly — 3.7V nominal is below the onboard regulator's minimum input.