If your car’s electrical system is a little finnicky, this $12 dongle plugs straight into your accessory outlet to help you diagnose battery and alternator problems, before they leave you stranded.

When the engine is turned off, the meter will show you the overall voltage and charge level of your battery, so you know when it might be time to buy a replacement. While you’re driving, it will also indicate when the battery is recharging or discharging, which can help you diagnose a malfunctioning alternator. You probably won’t keep it plugged in all the time, but for $12, it might be useful to add this to your tool chest. [INNOVA Battery and Charging System Monitor, $12]

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