Battery capacity is usually given in milliamp hour (mAh) or Amp hours.
The math is really easy if you want to drain a fully charged battery in 1 hour. A 1Ah (1,000mAh) battery can provide a steady one amp of current for one hour. A 2 Ah (2,000mAh) battery can provide a steady two amps of current for one hour.
- 1Ah battery providing 0.5A will take 2 hours to discharge.
- 1Ah battery providing 2A will take 30 minutes to discharge.
- 1Ah battery providing 0.1A will take 10 hours to dischatge.
Be careful of rated values
Exact battery properties vary by chemistry and manufacturing techniques. Always consult the manufacturers specifications, as long as they are a reputable company.
Too good to be true:
- Lots of low priced knock off batteries will claim outrageous capacity. One example is impossible to make 9,000mAh 18650 li ion battery sold on auction sites. Good chance it doesn’t even have 1000mAh.
- Lower currents, certain temperatures, etc. will give more promising results. The way the battery is actually used will likely result in a lower capacity than is claimed.
Amount of use:
- Capacity goes down as you charge/discharge batteries many times.
- Capacity goes down with age.
Ah/mAh with series batteries
Connecting batteries in series adds up voltage, but each battery still passes the total circuit current. So each one discharges (voltage drops) base on the current flow.
With 2 perfectly equal batteries connected in series, you will have twice the voltage of one of them but will only provide the same amount of current over time as one of them. That equals twice the total power of a single battery because power equals voltage times current (P=VI).
- 1.5V 1Ah battery can provide 1A of current for one hour.
- Two series 1.5V 1Ah batteries provide 3V and can provide 1A of current for one hour.
AH/mAh with parallel batteres:
The capacity (current over time) of batteries in parallel simply adds up.
If their capacities are the same, then 2 batteries can provide a certain amount of current for twice as long as a lone battery.
3 equal value parallel batteries can provide a certain amount of current for three times as long as a lone battery.
More topics to check out:
- Battery voltage state of charge SOC – From fully charged to discharged
- Battery C rate rating explained
- Series batteries for a higher voltage
- Parallel batteries for more current
- 001 Resistive component multimeter voltage-current-resistance measurements
- Brief switch controlled indicator LED circuit
- Brief capacitor charge and discharge through LEDs circuit
As an Amazon Associate I earn from qualifying purchases.