# Calculate battery discharging time?

Being far enough from everything about electrical engineering and so on, I'm sorry in advance for a dumb and possibly asked here in threads earlier such question.

I have only the next data on batteries:
- Battery Current Limiting Coefficient
- Battery Capacity

There's also an Average Discharge Current(A), but this variable is gotten from the tests of already used batteries and can be even negative (like -44.3), so I dont think I can use it.

I wonder can I calculate the battery discharge time (approximate time of battery life before full discharge) using given parameters? I found many formulae but there's always a lack of at least one element to use the function.

• What is BCLC ? || Discharge time = Battery capacity (in mAh or Ah) divided by discharge current (in mA or A). | You'll need to specify how you got eg average discharge current for it to be helpful. AND a negative average discharge current suggests that the battery was charging. Circuit. More words. ... . – Russell McMahon Oct 30 '19 at 13:06
• @RussellMcMahon BCLC belongs to current limit coefficient of the battery. The maximum charging current equals the value of "Battery Current Limiting Coefficient" multiplexed by "Battery Capacity". If the charging current is 5 A higher than the maximum charging current, the overcharge alarm is reported – Ison Oct 30 '19 at 13:19
• @RussellMcMahon thanks for explanation of negative discharge current. Now it makes sense – Ison Oct 30 '19 at 13:20

Battery discharge time is fairly easy to calculate in principle, assuming the load draws constant current. This means the load will always draw the same amount of current as long as the battery voltage is within the range allowed by the load specifications. "Load" is a general term for eveything powered by the battery.

You need to know how much current your load draws on average. Placing a voltmeter in series with the load will tell you the current, unit mA. If the number is negative, you hooked up the voltmeter the wrong way or something is off; maybe the battery is being charged from USB or a wall plug?

You also need to know the capacity of the battery, in unit mAh.

Now just divide the battery capacity by the current to get the battery time.

Example: 1000 mAh battery and 100 mA load gives 1000 / 100 = 10 hours of battery time.

It's common for circuits to draw slightly more when the battery is fresh and gives higher voltage, but we can simplify by using the average ("nominal") battery voltage. Some circuits also draw different amount of current depending on mode, such as sending radio packets, entering power-save or activating a display. The calculation must be done with the average current, or be carried out for each system mode separately.

A more advanced analysis would look at battery self-discharge rate, internal resistance, temperature, etc. For example, a coin cell battery will drain very quickly if put under heavy load, but last for years if used correctly. Anyway, the basic calculation should give a rough, slightly overestimated battery time.

• Thanks for the great explanation. Unfortunately, I have neither batteries nor voltmeter, just excel file with the data. But at least I realize now what to ask for. – Ison Oct 30 '19 at 14:00
• Battery capacity is specified in the battery datasheet (search online), or often even printed on the battery itself. But you positively need to know the current draw of the device. You mentioned "Average Discharge Current" which is the same thing. – Anders Petersson Oct 30 '19 at 14:08