Six degrees outside, seven in the morning, and my truck clicked instead of turning over. The nearest person with cables was 20 minutes away and already at work.

The little lithium jump pack in my trunk started it on the first try. That was three winters ago and I have used it on four other cars since.

What to look for

• Peak amps matched to your engine. Small four cylinder cars need far less than a V8. Buying for your engine instead of for the biggest number on the box saves money.
• A real cold cranking rating. Cold is exactly when you need it, and cold is exactly when a cheap pack underperforms.
• Cables long enough to reach both terminals without stretching across the engine bay.
• Reverse polarity protection. Non negotiable if anyone else might ever use it.

The habit that matters more than the device

Charge it twice a year. Mine lives in the trunk and self discharges slowly. A dead jump pack is worse than no jump pack, because you counted on it.

I put a reminder on the calendar for the first weekend of April and October. Takes an hour on the charger.

How to actually use it

1. Connect red to the positive terminal, black to the negative or to a bare metal bolt on the engine block.
2. Make sure the clamps are not touching each other.
3. Turn the pack on and wait a few seconds for it to detect the battery.
4. Start the car. If it does not start within a few seconds, stop and wait a minute before trying again.
5. Disconnect black first, then red.

What it will not do

It will not rescue a battery that is completely dead from a failed alternator. It gives a strong short burst, not sustained power.

If your car needs a jump every week, the jump pack is a symptom treatment. Get the battery and alternator tested, because the real problem is somewhere else.

Still, for the one cold morning a year, it pays for itself in the first tow truck you do not call.