Batteries
Battery Internal Resistance Calculator
The calculator turns the entered batteries values into internal resistance and keeps the practical caveats on the page.
Set up the Battery Internal Resistance case
Document whether open-circuit voltage and the other entries are measured, rated, assumed, or calculated.
Scope of the internal resistance result
The displayed internal resistance answers one bounded question: calculate battery internal resistance from a documented load test. Treat it as a case record rather than a general approval.
Battery Internal Resistance depends on battery chemistry, state of charge, temperature, age, and the discharge or charge rate.
If two cases differ in open-circuit voltage, save them as separate runs. A blended entry can hide the reason the internal resistance changed.
Source notes for Battery Internal Resistance
Collect Open-circuit voltage, Loaded voltage, and Test current from the same operating case before reading internal resistance.
- Open-circuit voltage
- Enter open-circuit voltage in V. Default shown: 12.8 V.
- Loaded voltage
- Enter loaded voltage in V. Default shown: 12.2 V.
- Test current
- Enter test current in A. Default shown: 20 A.
Interpreting Battery Internal Resistance
Use internal resistance as a checkpoint. If it drives a decision, compare a conservative Battery Internal Resistance case before accepting the number.
Changing open-circuit voltage while leaving loaded voltage fixed is a useful way to see which assumption controls the answer.
Formula notes for Battery Internal Resistance
A clean Battery Internal Resistance result confirms the arithmetic for internal resistance; it does not prove the equipment rating or source data is the right one.
Boundaries for internal resistance
Measure both voltages at the same state of charge and temperature.
- Bms cutoffs
- Temperature effects
- Voltage sag under load
Operating notes for Battery Internal Resistance
Battery Internal Resistance should be read with chemistry and state-of-charge notes. The same amp-hour value can represent a different usable-energy case at another discharge rate.
When internal resistance becomes an input to another worksheet, copy the value only after the units and source condition have been verified.
Records for open-circuit voltage
Attach chemistry, state of charge, temperature, and the test condition used for the Battery Internal Resistance entry.
If a later Battery Internal Resistance run changes only open-circuit voltage, label it as sensitivity work. Several changed conditions deserve a new baseline.
Keep screenshots or notes only when they identify the Battery Internal Resistance source values. A saved final number without entries is hard to audit.