Product Description

Easily turn your 18650 cells into a portable power bank using this parallel battery case. The enclosure integrates a management board with dual USB 5 V/2.4 A (max.) outputs and charging via USB-C or Micro-USB (5 V/2.1 A input), plus a 4-LED indicator for the energy level. Built for DIY-savvy users, the solution lets you assemble a robust external battery pack with capacity scaled to the number and quality of the cells used — all connected in parallel.

Warning (proper use):

– Use 18650 flat-top cells only, without a protection board, with internal resistance < 50 mΩ and discharge rate ≥ 1C.

– All cells must be in a similar state of wear and at similar voltages (3.3–4.2 V each) before assembly. Do not mix old and new cells and do not insert damaged cells.

– The enclosure is parallel: do not insert the “positive” of one cell with the “negative” of another; all cells share the same polarity on the rails.

– If the output becomes intermittent or any heating occurs, stop using the device and replace the cells immediately.

– Does not support USB-C Power Delivery; the USB-C port is for 5 V charging only.

– Product intended for users with basic knowledge of handling Li-ion cells.

Technical Details

• Battery type: 18650 Li-ion, 3.7 V nominal (flat-top, unprotected)
  – Internal resistance: < 50 mΩ
  – Recommended discharge rate: ≥ 1C
  – Operating voltage per cell: 3.3–4.2 V
  – Not compatible with button-top/protected cells.
• Configuration: parallel (total capacity increases, voltage remains 3.7 V nominal)
• Outputs: 2 × USB-A 5 V/2.4 A (max.)
• Inputs: USB-C and Micro-USB, 5 V/2.1 A (no PD, no high-voltage fast charge)
• Power display: 4 LEDs (voltage-based estimate; with weak cells the indicated level may drop quickly)
• Features: intelligent auto-shutdown when idle
• Material: Plastic + metal
• Dimensions: 10.3 × 8.0 cm
• Available colours: black, white, blue, green (some batches: red/blue/green/black)

Performance note: Cells meant for torches/radios with low current draw can suffer voltage sag under load, resulting in unstable power. For power-bank use, we recommend quality cells with higher current capability and stable voltage.

Important note about the 18650 market (”fantastic” capacities)

The 18650 market is crowded with products advertising misleading specifications. Listings claiming 10,000–30,000 mAh from a single 18650 are physically impossible. Realistic capacities for modern 18650 cells generally fall between 1,800 and ~3,600 mAh per cell; values above this threshold are either false or tied to modified/unsafe cells. So-called “30,000 mAh” cells often measure at only a few hundred mAh in reality (e.g., 100–500 mAh), typically re-wrapped old cells or “hollow” cells with minimal active material.

How to tell a genuine 18650 cell from one with fake specs:

• Realistic weight: a genuine high-capacity 18650 typically weighs ≈ 45–50 g. Fakes often weigh < 35 g due to reduced active material.
• Brand & full code: reputable manufacturers (e.g., Panasonic/Sanyo, LG, Samsung, Sony/Murata, Molicel) print model and lot codes (e.g., NCR18650, MJ1, 35E, VTC6). Generic cells marked “9900 mAh / 12000 mAh / 30000 mAh” without a proper code are suspicious.
• Protected vs. button-top: this product requires flat-top unprotected cells. “High-capacity” fakes frequently come as cheap button-tops; not suitable here anyway.
• Unrealistically low price: a genuine high-end cell won’t cost “pennies”. Large gaps from normal market pricing usually indicate bogus specs.
• Packaging and lot: beware of “no-name” shrink wraps without data; look for manufacture dates and consistency across cells.
• Behaviour under load: fake cells show heavy voltage sag and heat up even at moderate currents (e.g., 1–2 A).
• Internal resistance: measured with a dedicated tester, fakes typically have much higher IR (tens to hundreds of mΩ), limiting current and increasing heating.

How to verify capacity yourself (safely):

1. Charge the cell to 4.20 V with a suitable Li-ion charger.
2. Let it rest for 30–60 min to stabilise.
3. Perform a controlled discharge at 0.2–0.5 C (e.g., 700–1,800 mA for a 3,500 mAh cell) down to 2.75–3.0 V using a charger-analyser.
4. Read the measured capacity (mAh). Repeat 2–3 times and average.
5. Monitor temperature; if it becomes excessive, stop the test — the cell is non-compliant.

Practical recommendations for this power bank:

• Buy cells from reputable suppliers; avoid obscure “brands” with fantastic numbers.
• Do not mix cells of different brands/capacities or different wear levels.
• Avoid harvested cells from unknown packs unless you can test each one (capacity, IR, leakage).
• Aim for cells of 3,000–3,500 mAh with low IR for stable runtime and adequate current under load.

Package Contents

• 1× 18650 power bank enclosure (solder-free assembly) — batteries not included.