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Battery Charging Time Calculator

Charge time from state of charge, charger output, and the battery's accepted charge rate, plus the energy drawn from the source.

Inputs

Bank and charge source

Total capacity being charged, from the datasheet.

Where the bank is now, read from the inverter or BMS.

Where you want to stop. Charging above about 90% slows sharply in the constant-voltage phase.

Power available to the bank: charger rating, or expected solar production during the charge window.

Maximum the battery will accept, from the datasheet C-rate. The smaller of this and the charger output governs charge time.

Energy stored per unit supplied. 85-95% typical for lithium; lead-acid is lower.

Result

Charging time
1.6 hrs
Charging time
93 min
Charge power actually used
5.00 kW
Energy to add to the bank
7.00 kWh
Energy drawn from the source
7.78 kWh

What to check

  • State of charge from the BMS or inverter, not from voltage alone on lithium.
  • The battery's accepted charge rate (C-rate) from the datasheet; a bigger charger will not charge faster past it.
  • Charging efficiency from the inverter or charger datasheet; lead-acid is lower than lithium.
  • Real solar output during the charge window, not array nameplate, and whether the window is long enough in winter.
  • Constant-voltage taper: above roughly 80-90% state of charge the current drops, so actual time is longer than the constant-power figure.
  • Temperature limits on charging, especially for lithium below freezing.

Keep going

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Constant-power estimate. It ignores the constant-voltage taper above roughly 80-90% state of charge, temperature limits, and variable solar output, so treat it as a lower bound on time. Verify charge-rate limits, temperature windows, and protection against the manufacturer datasheet and the locally adopted National Electrical Code (Article 706).

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