RC Battery Runtime & Voltage Calculator

RC car battery voltage equals cells × per-cell voltage: LiPo is cells × 3.7 V nominal (cells × 4.2 V full), NiMH is cells × 1.2 V nominal. So a 2S LiPo is 7.4 V and a 6-cell NiMH is 7.2 V. The calculator below also estimates runtime and C-rating current; all results are estimates.

How to use the RC battery runtime & voltage calculator

Chemistry, cell count, capacity and C-rating come from your pack’s label. The optional continuous-current limit comes from your pack manual. Average current draw is different: it is not printed on the pack, so you measure or estimate it for your own vehicle and driving conditions. All fields start blank, so nothing is assumed for you.

1. Pick the chemistry. Choose LiPo or NiMH, as printed on the pack label.
2. Enter the cells in series. For LiPo this is the “S” number on the label (2S = 2 cells in series). For NiMH, count the cells or check the label.
3. Enter the capacity in mAh from the label. With these three fields filled in, you already get nominal voltage, plus full-charge voltage for LiPo.
4. Optional: enter the C-rating from the label to see the max continuous current calculated from it. Leave it blank to skip that output.
5. Optional: enter your average current draw in amps to get an estimated runtime. This number does not come from the pack: measure it or estimate it for your vehicle, setup and driving conditions. If you leave it blank, runtime is skipped; the tool still shows the voltages and max current and tells you to enter a draw for runtime.
6. Optional: enter the continuous-current limit from your pack manual. The tool shows it next to the calculated value and uses the lower of the two as the “limit to respect”. If your average draw is above that limit, you get an informational warning.

Once you have calculated, the results update as you edit any field. If you switch chemistry, the numbers you typed are kept and every output is recomputed.

How the numbers are calculated

The calculator uses four simple formulas. The sourced per-cell values used here are 3.7 V nominal and 4.2 V full charge for LiPo, and 1.2 V nominal for NiMH. Capacity and C-rating come from your pack’s label, and the optional continuous-current limit from your pack manual. Average draw is your own measured or estimated figure for your vehicle and driving.

1. Nominal pack voltage. LiPo: V_nom = cells × 3.7. NiMH: V_nom = cells × 1.2. Assumes the standard nominal value per cell.
2. Full-charge pack voltage. LiPo: V_full = cells × 4.2. NiMH: no sourced full-charge figure is used, so the tool shows “Varies by pack/charger. See your pack manual” instead of a number.
3. Estimated runtime (minutes): runtime_min = (mAh ÷ 1000) ÷ avg_draw_A × 60. Assumes the full rated capacity is delivered at a steady average draw. No usable-capacity derating is applied.
4. Max continuous current (A): I_max = (mAh ÷ 1000) × C. Calculated from the label’s C-rating only. It is not a safe-use approval.

Here is how cell count turns into pack voltage with these per-cell values:

To show the runtime and current arithmetic: if a 5,000 mAh pack averaged 10 A, runtime would be (5000 ÷ 1000) ÷ 10 × 60 = 30 minutes. With a label rating of 50C, the calculated max continuous current would be (5000 ÷ 1000) × 50 = 250 A. These numbers only illustrate the formulas. They are not a recommendation for any pack or draw.

Why your real runtime will differ

The runtime figure is an ideal estimate and is likely optimistic. Real current draw is not constant: it rises and falls with throttle use, so a single “average draw” can only approximate how you drive. The average draw you enter is your own measurement or estimate for your vehicle and conditions, so the result is only as good as that figure. Battery University also notes that losses at fast discharges reduce the discharge time. The calculator does not apply a correction factor, because no sourced derating value exists for it to use. Treat the result as an upper-end reference, not a promise.

Why a C-rating is not a safety approval

The max-current figure is simple arithmetic on the C-rating printed on the label. It does not mean that drawing that much current is safe for your pack, ESC, motor or vehicle. Your pack manual may state its own continuous and max current limits, and your ESC or vehicle manual may limit cell count or voltage. Those documents take priority. That is why the tool lets you enter the manual’s continuous limit and then shows the lower value as the limit to respect.

RC car battery 2S LiPo vs 7.2 volt NiMH: what the numbers say

A 6-cell NiMH pack works out to the familiar 7.2 volt figure: 6 × 1.2 = 7.2 V nominal. A 2S LiPo has two cells in series: 2 × 3.7 = 7.4 V nominal and 2 × 4.2 = 8.4 V at full charge. On paper, the nominal difference is 0.2 V.

That comparison is about voltage numbers only. This calculator does not claim a 7.2 V NiMH and a 7.4 V LiPo are interchangeable. Whether a pack works with your car depends on your ESC and vehicle manual, the connectors, charging and the chemistry’s own handling rules. If you are thinking about switching, start with our guide on whether you can replace NiMH with LiPo in an RC car.

As an RC car calculator, the tool works the same way for any cell count from 1 to 20. Pick the chemistry, type the cell count and read the nominal voltage. For LiPo, you also get the full-charge voltage.

Methodology & sources

The per-cell values and formulas come from these published references:

• Wikipedia: Lithium polymer battery: LiPo cells are about 4.2 V fully charged, with a nominal voltage of 3.6 or 3.7 V. 3.7 V is the nominal value used here.
• Battery University BU-409: Charging Lithium-ion: cross-check that lithium cells typically charge to 4.20 V per cell.
• Wikipedia: Nickel–metal hydride battery: NiMH cells nominally operate at 1.2 V per cell.
• Battery University BU-402: What is C-rate: a 1 Ah battery should provide 1 A for one hour, and at 2C it delivers 2 A for 30 minutes. These are the basis for the runtime and max-current formulas. The same page notes that fast discharges reduce discharge time.
• Your pack’s label and manual: chemistry, cell count, capacity and C-rating come from the label; the optional continuous-current limit comes from the pack manual.
• Your own measurement or estimate: average current draw is not a pack specification. It depends on your vehicle, setup and driving conditions, so you measure or estimate it yourself. Leave it blank and the runtime output is skipped.

Nothing you enter is sent anywhere; the calculation runs in your browser. We also cross-checked the 3.7 V nominal value against a Traxxas LiPo pack manual (part 68386-4), which lists 2S as 7.4 V and 3S as 11.1 V nominal. The tool deliberately leaves out a NiMH full-charge voltage, any usable-capacity percentage or derating, and any “safe” current threshold, because none of these comes from a manufacturer document. These per-cell values are reviewed at least once a year, and sooner if a manufacturer document contradicts them.

Last updated: October 2026

These figures are estimates for general reference only. A C-rating is not a safety approval; always follow the pack, charger, ESC and vehicle manufacturers’ manuals and stated limits before charging or using LiPo or NiMH packs.

FAQ

What voltage is a 2S LiPo?

Using the 3.7 V per-cell nominal value, a 2S LiPo is 2 × 3.7 = 7.4 V nominal. At the 4.2 V per-cell full-charge value it is 2 × 4.2 = 8.4 V.

Is a 7.2 V NiMH the same as a 2S LiPo?

No. A 6-cell NiMH pack is 6 × 1.2 = 7.2 V nominal and a 2S LiPo is 2 × 3.7 = 7.4 V nominal, a 0.2 V difference on paper. The calculator only compares the numbers and does not say the packs are interchangeable, so check your ESC and vehicle manual.

How is runtime estimated?

Runtime in minutes = (mAh ÷ 1000) ÷ average draw in amps × 60. It is an ideal estimate and likely optimistic, because real current draw changes with throttle use and fast discharges shorten the discharge time.

Is the max current from the C-rating a safe limit?

No. Max continuous current = (mAh ÷ 1000) × C is calculated from the label’s C-rating and is not a safety approval. Follow the current limits in your pack manual and your ESC and vehicle limits.

Why does the calculator show no full-charge voltage for NiMH?

There is no manufacturer-sourced full-charge figure per NiMH cell behind this tool, so it shows “Varies by pack/charger. See your pack manual” instead of guessing a number.

Related guides

• How Long Do RC LiPo Batteries Last? Cycles, Runtime and Lifespan
• How to Store RC LiPo Batteries Safely Between Runs
• Can You Replace NiMH With LiPo in an RC Car? What to Check First
• LiPo vs NiMH RC Battery: Power, Safety and Cost Compared
• How to Clean and Store a Nitro RC Car With After-Run Oil
• How Fast Do RC Cars Go? Top Speeds by Motor, Battery and Gearing