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RC Battery Charger Wattage Calculator

Estimate the output wattage a charger needs for a given cell count and charge current.

Charger Requirement

e.g. 0.85 — only used when the box above is ticked.

Result

Required output power
42W
Charge voltage
4.2V
4.2 V/cell max
Supply input (if efficiency set)
0W

Output power is charger-side. Supply input is only estimated when you provide an efficiency.

Formula

  1. 1.Charge Voltage = Cell Count × 4.2 V
  2. 2.Output Power (W) = Charge Voltage × Charge Current
  3. 3.Input Power = Output Power / Efficiency (only when provided)

Worked example

  1. 1.Inputs: 4S pack, 10 A charge.
  2. 2.Charge voltage = 16.8 V; output = 16.8 × 10 = 168 W — choose a charger rated above that.
  3. 3.At 85% efficiency the supply must deliver ≈ 198 W.

Assumptions and limits

  • Pick a charger with headroom above the computed wattage.
  • Dual-port or parallel charging changes the per-port requirement.

Related tools

FAQ

My 100 W charger is slow on 6S — why?

At 6S the charger needs 25.2 V × current; wattage limits force the current down.

Assumptions

  • Charge voltage = 4.2 V × cell count.
  • Supply input requires a stated efficiency — it is not assumed.