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Battery Life Calculator

Calculate how long a battery will last — enter mAh capacity and current draw, get runtime in hours and days with efficiency and discharge depth

mAh
90%
50% (LDO worst) 85% (typical) 100% (ideal)
80%
50% (conservative) 80% (Li-Ion safe) 100% (full)

Results

Enter battery capacity and current draw to see results

About This Tool

"How long will my battery last?" is the first question in every portable project — from Arduino sensors to power banks to IoT devices. The basic formula is simple: hours = mAh ÷ mA. But real-world runtime depends on regulator efficiency, discharge cutoff voltage, and whether you have multiple power modes. This calculator handles all of it. Enter your battery capacity, add one or more power modes (active, sleep, transmit), set efficiency and discharge depth, and get accurate runtime in hours and days. It also includes presets for common batteries (AA, AAA, CR2032, 18650, LiPo) and typical loads (Arduino, ESP32, Raspberry Pi). Whether you're sizing a battery for a solar sensor node, estimating power bank charges, or figuring out how often to replace CR2032s in a BLE beacon — this gives you the answer in seconds.

How to Use

1. Select a battery preset or enter custom capacity in mAh 2. Enter current draw in mA (or add multiple power modes with duty cycles) 3. Optionally adjust efficiency (default 90%) and discharge depth (default 80%) 4. See estimated battery life in hours and days 5. Click "Copy Link" to share your calculation

Frequently Asked Questions

How do I calculate battery life?
Divide battery capacity (mAh) by average current draw (mA) to get hours. For example, a 2000mAh battery powering a 50mA device lasts 2000 ÷ 50 = 40 hours. In practice, multiply by efficiency (~0.85–0.95) and discharge depth (~0.80) for realistic results.
What is battery efficiency and why does it matter?
Battery efficiency accounts for energy lost in voltage regulators, internal resistance, and heat. A typical switching regulator is 85–95% efficient; a linear regulator (LDO) is less. A 2000mAh battery at 90% efficiency effectively delivers 1800mAh. Always account for this in your calculations.
What is discharge depth?
Discharge depth is how much of the battery's capacity you actually use. Lithium batteries should not be drained below 20% (80% depth) to preserve cycle life. Alkaline batteries drop voltage as they discharge, becoming unusable before fully empty. Setting depth to 80% means you use 80% of the rated mAh.
How long does a CR2032 last?
A CR2032 has ~220mAh capacity. At 10µA (a typical BLE beacon), it lasts about 220 ÷ 0.01 = 22,000 hours ≈ 2.5 years. At 1mA continuous, it lasts about 220 hours ≈ 9 days. The calculator handles micro-amp loads — just enter 0.01 for 10µA.
How do I calculate battery life with sleep and active modes?
Use the duty cycle feature. If your device draws 80mA when active for 1% of the time and 0.01mA in sleep for 99%, the average is (80 × 0.01) + (0.01 × 0.99) = 0.81mA. Enter both modes with their duty percentages and the calculator averages them automatically.
How many times can a power bank charge my phone?
Divide power bank capacity by phone battery capacity, then multiply by efficiency (~0.85). A 10,000mAh power bank with a 4,000mAh phone: 10000 × 0.85 ÷ 4000 = 2.1 full charges.

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