RC Charger Wattage Calculator
Figure out how much charger wattage you actually need, and roughly how long a charge will take, based on pack size, cell count, and charge current. Works whether you’re charging one pack or several at once.
How this works
- Why 4.20V per cell, not 3.70V? A LiPo pack sits at its highest voltage right at the end of a charge (fully charged = 4.20V/cell), and that’s also when the charger is still pushing close to full current before it tapers off. That’s the real peak power draw moment, so sizing your charger against nominal voltage (3.70V/cell) can leave you short right when it matters — this calculator uses 4.20V/cell so the number reflects the charger’s actual worst-case load.
- Charging multiple packs at once (either on separate channels, or in parallel on a parallel-charge board) adds current, and since the packs are the same voltage, total wattage is just the per-pack wattage multiplied by how many packs you’re charging.
- Charge time is an ideal-case estimate assuming constant current the whole way. In reality, the last portion of a charge tapers off in the constant-voltage phase, so real-world charge time is usually a bit longer than this number.
Rounded up to a common charger wattage class, with headroom so the charger isn’t running at its absolute ceiling.
How it works: Per-Pack Watts = Cells × 4.20V × Charge Current. Total Watts = Per-Pack Watts × Number of Packs. Charge Time = (Capacity ÷ 1000) ÷ Charge Current × 60, in minutes.
Frequently Asked Questions
Should I match the charger wattage exactly, or go higher?
Go higher. Charger manufacturers list a maximum wattage, and running right at that ceiling doesn’t leave room for multiple channels, parallel boards, or slightly optimistic capacity ratings on your packs. Leaving meaningful headroom (the recommended size above already builds this in) keeps your charger from derating current.
Does charging multiple packs on one charger split the wattage?
It depends on the charger. Some chargers have a single shared power budget across all channels, so two packs charging simultaneously split the available wattage between them and each one charges slower. Others (especially dual/quad chargers with independent power supplies per channel) give each channel its own full wattage. Check your charger’s spec sheet for “shared” vs “independent” channel power.
What’s the difference between charge current in amps and C-rate?
C-rate is charge current expressed relative to capacity: 1C means charging at a current equal to the pack’s capacity (a 5000mAh pack at 1C = 5A), while 2C would be 10A. Most LiPo packs are safely charged at 1C unless the manufacturer specifically rates them for faster charging.
Does this apply to NiMH batteries too?
Not directly — this calculator uses LiPo/Li-ion’s 4.20V per cell peak charge voltage, while NiMH cells peak around 1.4–1.5V during charge and use a different charge termination method (delta-peak) entirely. For NiMH, you’d need to substitute the correct peak voltage per cell in the same basic formula.
Why is my actual charge time longer than the estimate?
This calculator assumes constant current for the entire charge, but LiPo charging tapers into a constant-voltage phase as the pack approaches full, where current gradually decreases. That tail end adds real time beyond the simple capacity-divided-by-current math.