Question 1

Why is it important to measure internal resistance (IR) in drone batteries?

Accepted Answer

Internal resistance is the primary indicator of a LiPo battery's health and ability to deliver power. As a battery ages, its internal resistance increases, which leads to higher voltage sag under load and excessive heat generation during flight.

By regularly calculating the IR of your drone batteries, you can identify when a pack is nearing the end of its useful life. This proactive monitoring helps prevent in-flight power failures, protects your expensive drone components from heat damage, and ensures optimal flight performance during high-current maneuvers.

Question 2

What does a high voltage sag reading mean for my FPV drone?

Accepted Answer

Voltage sag occurs when the battery voltage drops significantly the moment the motors demand high current. If you observe a large voltage drop during your flight or calculated tests, it indicates that your battery is struggling to keep up with the power demands of your drone.

High voltage sag results in sluggish throttle response, reduced flight times, and an increased risk of battery 'puffing' or failure. If your calculated sag is excessive, it is a clear sign that the battery's internal chemical structure has degraded and it may no longer be safe for high-performance flying.

Question 3

How do I safely measure voltage under load to use this calculator?

Accepted Answer

To get an accurate measurement, you need to compare the battery voltage while it is at rest (no load) to the voltage immediately after applying a known, significant current load. This is often done using a telemetry-equipped drone or a specialized battery load tester while the battery is fully charged.

Ensure that you perform these tests with caution. Only apply high-current loads for short bursts to avoid overheating the battery or damaging your electronics. Always use a reliable digital voltmeter or your flight controller's telemetry data to log the voltage before and during the throttle punch or load event.

Question 4

Can I save my results in this application?

Accepted Answer

This application operates as a privacy-focused, client-side utility and does not utilize local storage, cookies, or databases. All data remains in your computer's active memory for the duration of your current browser session only.

Because the app runs in a sandboxed environment without persistent storage, your calculated results will be cleared automatically when you refresh or close the browser tab. We recommend manually writing down your battery health stats or taking a screenshot of the results panel to track your battery maintenance over time.

Drone Battery Voltage Sag & Internal Resistance Calculator