Use a battery maintainer (trickle charger)

A battery maintainer delivers a continuous low-level charge that keeps the battery topped up without overcharging. It is the most reliable method for vehicles stored for weeks or months at a time.

Steps

1. Purchase a smart battery maintainer rated for your battery type (lead-acid, AGM, or lithium).
2. Connect the red clamp to the positive terminal and the black clamp to the negative terminal or a chassis ground point.
3. Plug the maintainer into a standard wall outlet.
4. Leave it connected for the duration of storage. The unit monitors voltage and charges only when needed.

Tips

• Look for units labeled "smart" or "automatic" -- these stop charging at full voltage and resume when it drops, preventing overcharge damage.
• A maintainer rated at 0.75-1.5 amps is sufficient for most passenger vehicles.
• Mount the unit near the battery and route the cord safely to avoid tripping hazards in the garage.