accessories

how to choose correct battery pack

If your device needs a peak of 40 Watts:

  • At 3.7V (1S): The battery must push \approx 10.8A.
  • At 7.4V (2S): The batteries only need to push \approx 5.4A.

so for high current, always GOOD to use higher voltage pack

Build Rules

  1. Battery Matching: Before installing the protection board (BMS), the batteries must be well-matched (voltage difference $\le$ 0.05V, internal resistance difference $\le$ 5m$\Omega$, capacity difference $<$ 30mAh). If the voltage is too high during power-up, the BMS may trigger protection and fail to operate. If cells are fully charged, discharge them to the required level before connecting the BMS. Batteries should be connected in parallel first, then in series.
  2. Wiring Sequence: Connect the B- wire to the main battery negative terminal first (use a short, thick wire for B-). Then connect the balance wires. Crucial: Unplug the balance wire connector from the BMS before soldering them to the pack.
  3. Balance Wires: Start from BC0 (connected to the main battery negative). BC1 connects to the positive terminal of the first cell series, BC2 to the second, BC3 to the third, and so on.
  4. Verification: After wiring, measure the voltage between each pair of adjacent balance pins. For Li-Po, it should be $<$ 4V; for LiFePO4, it should be $<$ 3.5V. Once verified, plug in the connector, then connect the charger and load negatives to C-. Use thick wires for B- and C- connections. The sequence is vital, regardless of wire colors.
  5. Final Check: Measure the total battery pack voltage versus the BMS output voltage. They must be equal for the protection board to be considered working normally.

wiring

battery pack examples

battery-packs-dat

ref

🔋 Common Lithium Battery Pack Combinations

  • 2S = 8.4V
  • 3S = 12.6V
  • 4S = 16.8V
Configuration Voltage (V) Full Charge Voltage (V) Description
1S1P 3.7V 4.2V battery-1s-dat Single cell
1S2P 3.7V 4.2V battery-1s-dat 2 cells in parallel
2S1P 7.4V 8.4V battery-2s-dat 2 cells in series
2S2P 7.4V 8.4V battery-2s-dat 4 cells total (2 series × 2 parallel)
3S1P 11.1V = 12V 12.6V battery-3s-dat Common for RC and drones
3S2P 11.1V 12.6V battery-3s-dat 6 cells total
4S1P 14.8V 16.8V Laptop batteries, power-tools-dat
4S2P 14.8V 16.8V Higher capacity variant
5S1P 18.5V 21.0V Electric tools
5S2P 18.5V 21.0V Longer runtime tools
6S1P 22.2V 25.2V Drones, high-power packs
6S2P 22.2V 25.2V More capacity, same voltage
7S1P 25.9V 29.4V E-bikes, mid-size packs
7S2P 25.9V 29.4V E-bikes, scooters
10S1P 37V 42.0V Standard for e-bike packs
10S2P 37V 42.0V Common e-bike configuration
13S1P 48.1V 54.6V High-voltage e-bike pack
13S2P 48.1V 54.6V E-bikes, scooters
14S1P 51.8V 58.8V Some 52V e-bike packs
14S2P 51.8V 58.8V Higher capacity

why one bad 18650 battery will ruin other paralled batteries

How it ruins other paralleled batteries:

  • Constant Discharging of Healthy Cells: Healthy cells in parallel will try to "charge" the bad cell that is at a lower voltage. This means the good cells are constantly discharging into the bad cell, even when no external load is connected. This continuous drain can over-discharge the healthy cells, reducing their lifespan and capacity.
  • Overheating and Safety Risks: The bad cell, due to higher internal resistance or being constantly charged by other cells, can overheat. This heat can transfer to adjacent healthy cells, potentially damaging them or even leading to thermal runaway in severe cases, which is a significant safety hazard (fire or explosion).
  • Reduced Overall Pack Performance: The overall capacity and current delivery capability of the pack will be severely limited by the weakest cell. The pack will perform as if all cells are as bad as the faulty one.
  • Accelerated Aging of Healthy Cells: The constant stress of trying to compensate for the bad cell accelerates the aging process of the healthy cells.

can 18650 lihtium battery be soldered by soldering iron?

  • Heat Damage: Lithium-ion cells are sensitive to heat. Excessive heat from a soldering iron can:

    • Damage the internal chemistry of the cell, reducing its capacity, lifespan, and performance.
    • Melt or damage the internal safety components like the pressure vent or PTC (Positive Temperature Coefficient) switch.
    • In extreme cases, lead to thermal runaway, which can cause the battery to vent, catch fire, or even explode.

  • Difficulty: The positive and negative terminals of 18650 cells are often made of materials (like nickel or steel) that can be difficult to solder to without specialized flux and a powerful iron. Prolonged heating to achieve a good solder joint increases the risk of heat damage.

  • Safety Risks:

    • Accidentally short-circuiting the battery with the soldering iron tip or solder can cause extremely high currents, leading to sparks, burns, and battery damage.
    • Overheating can release flammable and toxic gases.

Recommended Alternatives:

  • Spot Welding: This is the industry-standard method for connecting 18650 cells. Spot welders deliver a very high current for a very short duration, creating a strong weld with minimal heat transfer to the cell's internals.
  • Battery Holders: Using appropriate battery holders allows for connections without soldering directly to the cells. This is a safer option for many DIY projects.
  • Pre-tabbed Cells: Some 18650 cells are available with nickel tabs already spot-welded to the terminals. These tabs are much easier and safer to solder to.

FPV power battery

Balance Connector

  • 2S battery = 2 cells in series → total 2 voltages to monitor (Cell 1 & Cell 2).
  • The 3 pins are:
    • Pin 1 (B-) → negative of first cell / main ground.
    • Pin 2 (C1) → middle point between cell 1 and cell 2.
    • Pin 3 (B+) → positive of second cell / total pack voltage.
  • This lets a balance charger measure each cell individually.

"Powerful" battery

1. Upgrade to Higher Cell Count (More Voltage)

  • Switch from 2S (7.4V) to 3S (11.1V) or 4S (14.8V) for more motor RPM and torque.
  • ✅ Check compatibility of your ESC and motor before upgrading.
    • If not rated for higher voltage, you risk burning them out.

Pros:

  • Significant performance boost
  • Higher speed and torque

Cons:

  • Can overheat/damage components
  • May require stronger drivetrain

2. Increase Battery Discharge Rate (C-Rating)

  • Higher C-rating = more current output, improving throttle response and torque.

Example:

  • 2S 5000mAh 20C → 5A × 20 = 100A max discharge
  • 2S 5000mAh 50C → 5A × 50 = 250A max discharge

Pros:

  • Better throttle response
  • Handles load more effectively (climbing, off-road)

Cons:

  • Higher cost
  • May be slightly heavier

3. Increase Capacity (mAh)

  • Higher mAh = longer run-time and less voltage sag under load

Example:

  • Upgrade from 2200mAh to 5000mAh for more endurance

reference images

Capacity Grading (Testing)

First, connect the cells in parallel and charge them fully. Then connect them in series (e.g., in groups of 24) and perform constant current discharge. You will need a BMS (like JK BMS) to measure capacity. Each time a cell triggers protection (low voltage), mark its capacity, remove/replace it, and continue until all cells have been tested.

Recommended tool: EBC-A10H Battery Capacity Tester (Charge/Discharge, Electronic Load, 5A Charge / 10A Discharge).

YR1035+

unbalance Series and Parallel

You have a battery configuration: 3P + 6P + 6P in series.

  • 3P group = 3 cells in parallel
  • 6P groups = 6 cells in parallel
  • Series connection → pack is 3S

Even though some groups have more cells, the smallest parallel group (3P) limits the total usable capacity.

1. Discharge Behavior

  • Current is the same through all series groups.
  • Example: load draws 9A total:
    • 3P group → 9A ÷ 3 = 3A per cell (high stress)
    • 6P groups → 9A ÷ 6 = 1.5A per cell (lighter load)
  • ✅ 3P cells drain faster.
  • ❌ Pack is considered “empty” when 3P group is fully discharged, even if 6P groups still have charge.

2. Charge Behavior

  • Charger applies current evenly through series groups.
  • Example: 9A charging current:
    • 3P group → 9A ÷ 3 = 3A per cell
    • 6P groups → 9A ÷ 6 = 1.5A per cell
  • ✅ 3P group reaches full voltage first.
  • ❌ Charger stops when 3P group is full → extra cells in 6P groups aren’t fully used.

3. Key Effects

  1. Capacity wasted: Extra cells in larger parallel groups are underutilized.
  2. Unbalanced stress: Smaller parallel group wears out faster.
  3. Reduced lifespan: Smallest group limits whole pack life and capacity.

4. Best Practice

  • Ensure all parallel groups in series have the same number of cells.
  • Example: redesign as 3S6P → full 18Ah usable capacity instead of being limited to 9Ah.

✅ Summary:

In series packs, the smallest parallel group determines the usable capacity. Extra cells in larger groups are underused, and the smaller group experiences higher current stress, reducing overall pack efficiency and lifespan.

APPs

common apps - Electric-tools-dat - drone-battery-dat

ref

Table of Contents

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