Battery charge time calculator
How long a battery takes to charge at a given current.
Fill in the fields and the result will appear here automatically.
Estimate the time to add a specified amount of charge at a constant battery current. This is a charge balance, rather than a prediction of a particular charger's complete cycle. Enter the amp-hours still needed; the default treats the entire stated capacity as needing replenishment. Here η is the fraction of supplied charge retained by the battery, not the charger's energy efficiency. Initial state of charge, voltage stages and current taper are not separate inputs.
How it works
Formula and logic
A current I supplies I·t Ah in t hours. Retained charge is C = I·t·η/100, so t = 100C/(Iη). Charge supplied by the charger is 100C/η. Voltage is absent from this model: an Ah balance does not describe energy losses in Wh.
Example
Adding 100 Ah at 10 A with η = 100% takes 10 h. At η = 80%, the source supplies 125 Ah over 12 h 30 min. Adding only 50 Ah at 10 A and 100% takes 5 h.
Fields and units
- Charge to add — Ah
- Charging current — A
- Retained charge fraction η — %
How to use
- — Enter the charge to add in Ah; calculate the remaining Ah yourself for a partial recharge.
- — Enter the constant current actually reaching the battery in A.
- — Use η between 1 and 100% for this battery and charging regime. 100% represents ideal charge retention.
- — Compare the calculated hours with the manufacturer's charging stages; the hours-and-minutes display rounds to a minute.
Method and limitations
- Calculation method
- Formula and logic
- Data or methodology source
- Victron Blue Smart IP22: charging stages and battery current — product-specific manual
- Limitation
- Constant-current charge model. It does not determine permissible charging current, voltage, temperature or termination; use the specifications for the actual battery.
FAQ
How does charging time differ from battery run time?
Charging uses current and charge to add in Ah. Run time at a specified power uses energy in Wh, so it also needs voltage, depth of discharge and conversion losses.
How much time should I add for the final charging stage?
There is no universal multiplier. Current during absorption or constant-voltage charging depends on battery chemistry and the charger's algorithm. This page does not integrate that current profile.
Can I enter the charger's energy efficiency?
Not directly. η here compares retained Ah with supplied Ah. Energy efficiency compares energies and may involve different voltages. No single charge-retention value applies to every battery.
Are the starting charge and a zero current handled?
Starting state of charge is not an input. Enter the Ah still needed for a partial recharge. Charge to add and current must be positive; zero current cannot give a finite replenishment time.