How to Keep a Car Battery Healthy When You Are Not Driving
If you go on a long trip, leave a car parked for weeks or own a vehicle you rarely use, the battery slowly discharges. Left too long, it can drop so low that it cannot be recharged properly and needs replacing. A few simple steps can prevent that.
Short version: drive the car for at least 20 to 30 minutes every week or two, or connect a smart battery maintainer. For storage longer than a month, disconnect the negative terminal.
Why a parked battery goes flat
Every battery loses a little charge on its own over time, and heat makes it happen faster. A modern car also has electronics that draw a small amount of current even when switched off, such as the alarm, the clock and the engine control unit's memory. Over weeks, that adds up.
If the battery stays flat, lead sulfate crystals can harden on the plates, making it harder to recharge. That permanent damage is called sulfation.
Option 1: drive it regularly
The simplest solution is a proper drive every one to two weeks. A short trip around the block is not enough. Aim for 20 to 30 minutes at a steady speed so the alternator can fully top up the battery.
Option 2: use a battery maintainer
A smart battery maintainer, sometimes called a trickle charger, keeps the battery topped up without overcharging it. Look for one designed for automatic float charging, and follow the instructions. In a hot country, a small solar maintainer placed on the dashboard can also work for cars parked outdoors, though the output is small, so check that the model suits your battery.
Option 3: disconnect the battery
If the car will sit for more than about a month, disconnect the negative terminal. This stops small drains. Before you do:
- Check your manual. Some cars lose settings such as radio codes or need to relearn idle and window settings.
- Switch everything off and take the key out.
- Use the correct spanner and disconnect the negative cable first. Tuck it away so that it cannot touch the terminal.
Check the battery voltage every month or so with a multimeter. A fully charged battery reads about 12.6 V. If it falls to about 12.4 V or lower, recharge it.
Storing a battery that is out of the car
- Clean the case and terminals.
- Charge it fully.
- Keep it in a cool, dry, well-ventilated place off bare concrete floors, away from flames and direct sun.
- Recheck the voltage monthly and top it up when needed.
Other tips
- Park in the shade or a garage. Heat speeds up self-discharge. See how heat affects car batteries.
- Do not leave lights, chargers or accessories connected.
- Keep the terminals clean and tight.
- Have the battery tested before a long period of storage, particularly if it is more than three years old.
If the battery is already flat
A jump-start may get you moving, but a deeply discharged battery is often damaged. Follow our jump-start guide and then have the battery tested. If it keeps going flat, read why does my car battery keep dying? for other causes.