Advanced LiPo Internal Resistance Calculator

1. Voltage & Current Metrics

Open Circuit Voltage ($V_{oc}$)

Resting pack voltage before load (e.g., 16.8V for 4S).

Loaded Voltage ($V_{load}$)

Voltage measured immediately under high current load.

Load Current ($I_{load}$ in Amps)

Current drawn during test application.

2. Pack Architecture

Cell Count (S Series)

Number of cells in series configuration.

Capacity (mAh)

Total pack milliamp-hour rating.

Discharge C-Rating

Manufacturer continuous rating.

3. Execution & Presets

Verify your telemetry or bench test parameters before submitting for analysis. Ensure secure low-resistance probe connections.

Example Preset Loaded: 4S LiPo pack tested at 40A load current.

Formula Used

The internal resistance of a Lithium Polymer (LiPo) battery pack is derived using Ohm's Law by observing the voltage sag under a known heavy load:

$$R_{total} = \frac{V_{oc} - V_{load}}{I_{load}}$$

To determine the individual cell resistance ($R_{cell}$), the total pack resistance ($R_{total}$) is divided by the total number of series cells ($N_{cells}$):

$$R_{cell} = \frac{R_{total}}{N_{cells}}$$

How to Use This Calculator

Measure the resting open-circuit voltage ($V_{oc}$) of your fully charged LiPo pack using a digital multimeter or telemetry system.
Apply a calibrated, heavy constant current load ($I_{load}$) and record the immediate sagged voltage ($V_{load}$).
Input your cell count configuration and pack specifications into the respective fields.
Click the calculation button to instantly analyze pack health metrics, resistance levels, and estimated power dissipation.

Comprehensive Guide to LiPo Internal Resistance

Lithium polymer batteries are the backbone of modern remote-controlled models, FPV drones, and various portable high-draw electrical systems. Understanding internal resistance (IR) is crucial for evaluating battery performance, thermal efficiency, and overall lifespan. Internal resistance acts as an inherent restriction to electron flow inside the chemical structure of the cell. As packs age, experience physical trauma, or undergo deep discharges, chemical degradation increases this internal resistance parameter significantly.

High internal resistance directly causes excessive voltage sag under heavy throttle or load conditions. This sag reduces peak available power output and forces the pack to dissipate energy internally as heat. Elevated heat buildup accelerates chemical wear, leading to puffed packs and premature cell failure. Routine monitoring using precision calculators allows operators to track degradation patterns, match cells accurately, and retire unsafe battery packs before catastrophic thermal runaway events occur.

Frequently Asked Questions

For standard high-performance multirotor LiPo batteries, individual cell IR values under 5 milliohms are considered excellent. Values between 5 and 10 milliohms indicate normal wear, while values exceeding 20 milliohms suggest severe degradation.

Electrolyte viscosity increases at lower temperatures, slowing down ion transfer and raising internal resistance. Testing should ideally take place at room temperature for consistent results.