How do I check the remaining battery life on my car?
In short: test the 12-volt battery with a voltmeter and a load test, and check the high-voltage battery’s state of charge and health using the car’s display or the manufacturer app.
Two battery systems, two checks
Most modern cars rely on a conventional 12-volt battery to power electronics and starting, plus a high-voltage battery for propulsion in hybrids and electric vehicles. Each has different indicators of remaining life. This guide covers how to verify both, from simple instrument readings to professional diagnostics.
Check the 12-volt starter battery
What to test on the standard 12V battery that powers electronics, lights, and starting, and how to interpret the results.
- Use a digital voltmeter or multimeter to measure resting voltage with the car off; aim for about 12.6–12.8 volts. If it sits near 12.0–12.4 volts, the battery is discharged and may need charging or replacement.
- Conduct a load test or battery test using a load tester; apply the rated load for 10–15 seconds and observe the voltage; a healthy battery should stay above roughly 9.6–10.0 volts under load (exact thresholds vary by manufacturer).
- Check the charging system voltage with the engine running; typical alternator output is about 13.8–14.4 volts which shows the alternator is charging the battery.
- Inspect physical condition and connections: look for a swollen case, leaks, corrosion on terminals, or loose/corroded cables; poor connections can imitate a weak battery.
- Consider age and symptoms: most 12V batteries last 3–5 years depending on climate and use; have a professional test or replace if you notice hard starting, dim lights, or warning lights.
Conclusion: Regular 12V battery checks help prevent unexpected breakdowns, and maintaining proper voltage and clean connections is key to reliability.
Check the high-voltage battery (EVs and hybrids)
In electric and plug-in vehicles, the battery’s state of charge and health are shown differently and are more integrated with range estimates and charging data. Follow these checks for practical diagnostics.
- Check the vehicle’s instrument cluster for State of Charge (SOC) and estimated range; many EVs display SOC as a percentage and a predicted driving range. Some hybrids also show SOC for the high-voltage pack.
- Use the manufacturer’s mobile app or connected services to monitor SOC, charging status, and sometimes battery health metrics; apps often provide remote monitoring and alerts.
- Look for a battery health or SOH (State of Health) readout if the vehicle offers it in the UI or app; SOH indicates how much of the original capacity remains, often shown as a percentage or color gauge.
- Monitor charging behavior and indicators: during charging, the vehicle may log charging rate, state of charge, and any interruptions; unusual drops or failures should be checked.
- Be mindful of temperature and range effects: extreme heat or cold can reduce effective range temporarily; if range seems too low for a full charge, consider a diagnostic check or preconditioning usage.
Conclusion: For EVs and hybrids, SOC and SOH via the dash and app provide the most actionable snapshot of battery life, while independent testing is less common than for the 12V battery.
Using diagnostic tools and professional help
When in doubt or dealing with high-voltage systems, seek professional testing and diagnostics.
- OBD-II scanner with battery data: Some scanners can read charging-system voltage and battery module data; access to high-voltage data may be limited by the vehicle and require specialized software.
- Dealership or certified technician: For high-voltage systems and battery management hardware, a trained technician can perform a full battery test, diagnostics, and safe servicing.
Conclusion: A professional battery test can confirm health and determine if a replacement is needed or if there is a fault in charging or the battery management system.
Tips to extend battery life
Simple habits that help preserve both 12V and high-voltage batteries between checks.
- Drive regularly or use a battery maintainer/trickle charger if the vehicle sits idle for extended periods; this keeps the 12V battery topped up and reduces sulfation.
- Keep battery terminals clean and tight; apply corrosion protection where needed; inspect for loose connections.
- Protect the high-voltage battery from extreme temperatures via vehicle preconditioning and parking in shade or garage when possible; temperature affects both battery health and performance.
- Follow the owner's manual for maintenance and service intervals; schedule battery checks at recommended service milestones.
Conclusion: Proactive care, cautious driving patterns, and timely maintenance extend battery life and help avoid unexpected failures.
Summary
Modern cars rely on two battery systems: the standard 12-volt battery and the high-voltage traction battery in hybrids/EVs. For the 12V battery, use a voltmeter, a load test, and check the charging voltage to assess health. For EVs and hybrids, rely on the dashboard/infotainment SOC and range, along with the manufacturer's app for additional health metrics, and seek professional help for comprehensive diagnostics. Regular maintenance and awareness of signs of weakness keep you prepared for any drive.
