If you’re interested in DIY battery projects, this guide shows how I built a 4S10P (14.8V nominal) battery pack using 40 pcs of 18650 Li-ion cells and a Daly BMS. This kind of pack can be used in power banks, solar storage, e-bikes, or portable backup power systems.

Why Li-ion 18650 Cells?

The 18650 Li-ion cell (18mm × 65mm) is one of the most popular rechargeable batteries.

✔ High energy density
✔ Good cycle life (500–1000 cycles depending on quality)
✔ Widely available & affordable
✔ Used in laptops, EVs, and power tools

Voltage profile:

• Nominal: 3.6V
• Fully charged: 4.2V
• Minimum safe discharge: 2.8–3.0V

Components I Used

• 40 x 18650 Li-ion cells (3000mAh each → ~30Ah total when in 10P)
• Daly 4S BMS (Li-ion type, not LiFePO₄!)
• Nickel strips (0.15–0.2mm for current handling)
• Spot welder (for cell interconnections)
• XT60 connectors
• Heat shrink tubing
• Multimeter + basic tools

What Is BMS?

A BMS stands for Battery Management System. It’s an electronic system that manages and protects rechargeable batteries — especially in packs like your LiFePO4 8S setup.

Key functions of a BMS:

• ✅ Overcharge protection (prevents damage from too high voltage)
• ✅ Over-discharge protection (prevents deep discharge that can ruin cells)
• ✅ Short-circuit protection (cuts off power in case of a fault)
• ✅ Cell balancing (keeps all cells at the same voltage to extend lifespan)
• ✅ Temperature monitoring (some advanced BMSs monitor heat to avoid thermal issues)

Battery Configuration: 4S10P

To reach both higher voltage and capacity:

• 10 cells in parallel = 1 group (~3.6V, ~20–25Ah)
• 4 groups in series = 4S pack (~14.4–14.8V nominal, ~16.8V full charge)

⚡ Final Specs:

Energy: ~300–370Wh

Voltage: 14.8V nominal (16.8V full, ~12V empty)

Capacity: ~20–25Ah (depends on cell grade)

Circuit Diagram:

Step-by-Step Assembly

1. Planning the Layout

• I grouped the cells into 4 parallel blocks of 10 cells each (10P).
• Arranged them in a rectangular layout for easier wiring.

2. Spot Welding the Cells

• Used nickel strips to connect 10 cells in parallel.
• Then connected the 4 parallel groups in series (positive to negative).
• Checked polarity carefully at each step.

3. Installing the Daly 4S BMS

• Connected main positive & negative leads to the pack.
• Wired balance leads to each cell group (B1, B2, B3, B4, B+).
• The Daly BMS provides:
  • Overcharge / over-discharge protection
  • Short-circuit protection
  • Balancing between groups

4. Final Checks

• Total pack voltage should read ~14.4–15.0V (depending on cell state).
• Each group should have similar voltage (within 0.05V ideally).

5. Wrapping & Connectors

• Wrapped the battery with heat shrink tubing.
• Added XT60 connectors for easy use.

Testing the Pack

• Connected to a DC load & 150W inverter.
• The pack delivered stable power at ~14.8V nominal.
• BMS worked properly during charge/discharge.

DALY BMS:

The Daly K-Series Smart BMS is a powerful and intelligent Battery Management System designed for lithium iron phosphate (LiFePO₄) and lithium-ion batteries. It supports 3S to 24S configurations and is available in 40A, 60A, and 100A versions, making it ideal for a wide range of applications including electric vehicles, solar energy storage, and backup power systems.

With built-in communication options like CAN, RS485, and UART, users can monitor and adjust settings in real time via a mobile app or PC software.

Applications

Where you can use this 14.8V Li-ion battery pack:

• DIY power banks
• Solar energy storage (with 16.8V charging system)
• E-bikes / scooters (with 14.8V controllers)
• Laptop / tool battery replacement packs
• Portable backup systems

Tips for Builders

• Use a spot welder, not soldering, to avoid overheating cells.
• Make sure to buy matched cells (same capacity & brand if possible).
• Double-check BMS type → for Li-ion (4.2V max per cell), not LiFePO₄.
• First charge should be done slowly (balance charge if possible).

18650 Li-ion Battery Cell – Detailed Guide

The 18650 is the most widely used cylindrical lithium-ion cell in the world. Its name comes from its dimensions:

• 18 mm diameter
• 65 mm length

First popularized in laptops and flashlights, 18650 cells are now a backbone of electric vehicles (Tesla uses them), power tools, solar storage, and DIY battery packs.

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Chemistry Types of 18650 Cells

Not all 18650s are the same. They come in different Li-ion chemistries, each with trade-offs between capacity, power, and safety.

1. ICR (LiCoO₂ – Lithium Cobalt Oxide)
   • High energy density
   • Moderate current capability
   • Lower cycle life (~500)
   • Example: Older laptop batteries
2. NMC / NCA (Nickel Manganese Cobalt / Nickel Cobalt Aluminum)
   • High energy density and high power
   • Widely used in EVs (Tesla, Panasonic, LG)
   • Cycle life ~800–1500 cycles
   • Balanced performance
3. IMR (LiMn₂O₄ – Lithium Manganese Oxide)
   • Safer & more stable than cobalt cells
   • High discharge current (good for power tools)
   • Lower energy density

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Electrical Characteristics

• Nominal Voltage: 3.6–3.7 V
• Full Charge Voltage: 4.2 V
• Minimum Voltage: 2.5–3.0 V (don’t go lower, or cell can be damaged)

Capacity

• Varies by brand and chemistry
• Typical range: 1500 mAh → 3500 mAh
• High-capacity cells (≥3000 mAh) usually have lower max discharge current

Discharge Rate (C-Rating)

• Expressed as “C” = multiple of capacity
• Example: A 2500 mAh cell rated 10C = 25A continuous discharge
• High-drain cells (like Sony VTC5A, Samsung 25R) are popular in vaping, EVs, and power tools

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Cycle Life

• Good quality cells: 500–1000 cycles
• EV-grade cells: 1000–2000 cycles
• Depends on:
  • Depth of discharge (DoD)
  • Charge/discharge current
  • Operating temperature

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Physical Features

• Flat top vs button top → Button tops are often used in flashlights, flat tops in packs.
• Protected vs unprotected → Some have a tiny PCB with over-charge/discharge protection. For battery packs, usually unprotected flat-tops are used.

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Safety Considerations

Li-ion cells store a lot of energy in a small space. Improper use can lead to fire or explosion.

• Never charge above 4.2 V
• Never discharge below 2.5 V
• Use a BMS (Battery Management System) in packs
• Avoid short-circuiting (instant heat & venting)
• Store at ~3.7–3.8 V if unused for long periods

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Applications

1. Consumer electronics → Laptops, flashlights, power banks
2. Electric vehicles (EVs) → Tesla used millions of 18650 cells before moving to 21700
3. Energy storage → DIY powerwalls, solar batteries
4. E-bikes / scooters
5. Power tools → drills, saws, welding packs

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Popular 18650 Cell Models

• Samsung 25R – 2500 mAh, 20A continuous
• LG HG2 – 3000 mAh, 20A
• Sony VTC5A – 2600 mAh, 25A continuous
• Panasonic NCR18650B – 3400 mAh, 5–7A (great for capacity, not high current)

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Summary Table

Spec	Typical Range
Size	18 × 65 mm
Nominal Voltage	3.6–3.7 V
Max Voltage	4.2 V
Min Voltage	2.5–3.0 V
Capacity	1500–3500 mAh
Energy (per cell)	~5–12 Wh
Cycle Life	500–1000+
Chemistry Options	ICR, IMR, NMC, NCA, LiFePO₄
Max Discharge Rate	5A → 30A (depends on model)

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