Free · Designed in Canada
Free car battery tools
Two quick calculators for common 12 V battery questions. Each one uses the figures one of our Learn articles cites, shows its sources, and works as a plain chart or table if JavaScript is off. They're estimates, not battery tests.
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Car battery voltage checker
Enter a resting voltage and the battery type, flooded or AGM, and see roughly how charged it is and what to do. Uses East Penn's published chart.
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How long can my car sit?
Enter the battery's amp-hours and the car's parked draw in milliamps, and see how many days a full battery takes to reach half charge, with the working shown.
How these tools work
- Every number has a source. The tools only use figures the matching article already cites, and each tool lists those sources.
- Nothing you type leaves your browser. The arithmetic runs on the page. We count that a tool was used, and which rough band the answer fell in (for example "12.4–12.6 V"), never the numbers you entered.
- They're estimates. A voltmeter reading shows charge, not health, and a drain calculation assumes a healthy, full battery. For a real answer about a battery's health, a load test on a fully charged battery is the check.