Batteries
Battery Voltage Sag Calculator
Battery Voltage Sag is a worksheet for comparing one electrical condition at a time, with the result tied to its inputs.
Build the Loaded voltage case
Small unit changes can move loaded voltage; confirm scale before using the result.
The Battery Voltage Sag equation
A clean Battery Voltage Sag result confirms the arithmetic for loaded voltage; it does not prove the equipment rating or source data is the right one.
Before entering sag at load
On Battery Voltage Sag, confirm decimal placement and unit scale before using loaded voltage; small prefixes can move an electrical result by orders of magnitude.
- Open-circuit voltage. Example value: 12.8 V. Enter open-circuit voltage in V.
- Sag at load. Example value: 0.7 V. Enter sag at load in V.
When open-circuit voltage is uncertain, run a low and high case instead of hiding that uncertainty in one entry.
When your notes point to Battery Internal Resistance, open it after saving this baseline so the two cases do not get mixed.
Detail checks for loaded voltage
Battery Voltage Sag 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 loaded voltage becomes an input to another worksheet, copy the value only after the units and source condition have been verified.
Pre-use check for Battery Voltage Sag
- Review zero or near-zero denominators before trusting a very large answer.
- Do not combine different equipment, time periods, or connection types in one run.
Notes to save with Battery Voltage Sag
Attach chemistry, state of charge, temperature, and the test condition used for the Battery Voltage Sag entry.
| Input set | Open-circuit voltage, and Sag at load |
|---|---|
| Result | Loaded voltage |
| Condition note | Transient and steady-state sag can differ. |
Common Battery Voltage Sag questions
How should multiple scenarios be compared?
For Battery Voltage Sag, keep the baseline unchanged, duplicate the case, and adjust one uncertain value at a time so the reason for the difference stays visible.
Should nameplate and measured values be mixed?
Only mix nameplate and measured values in Battery Voltage Sag when that mix represents the actual case. Otherwise keep them in separate runs.
When should this be run again?
Run a new Battery Voltage Sag case when the source condition changes, such as voltage, load, rate schedule, temperature, component, connection, or period.
What should be recorded with the answer?
Save the Battery Voltage Sag inputs, unit basis, operating case, and result note so loaded voltage can be reproduced later.