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Check The Juice
Clean crusty deposits from inside the battery posts and terminals. That ensures the engine’s starter is receiving a full charge, says AAA-certified master technician Michael Calkins. Nothing? Ask another hiker for a jump. If no one is around, call AAA. No cell reception? Don’t worry. As long as the dashboard warning lights flash when you turn the key—indicating the battery has some juice—you have options.
Warm the battery
If you think subzero temps (and not the overhead dome light) drained the battery, you can try warming it up (at 5°F, a lead-acid battery produces only half of its normal cranking power). Calkins recommends removing the battery from the engine block and placing it in a pot of hot (not boiling) water, submerged to within two inches of the battery top. Don’t fully immerse it, or place a heat source directly under the pot. Hot water bottles and bladders are less effective, but will still warm up the internal plates. After an hour, try starting the car. Never place a stove or flames near a battery being charged or jumped; it could ignite hydrogen gases.
If you drive a manual (stick shift) car, you can push-start it if the battery retains enough reserve power to activate the car’s computer, Calkins says. Shut off the radio, heat, and anything electrical, turn the key to the ‘on’ position, and press down the clutch as you shift into second or third gear. Release the brake pedal, and tell your friends to start pushing. As the car speeds up to 5 or 10 mph (downhill helps), release the clutch, let the engine turn, and give it gas. Note: This doesn’t work with an automatic because the transmission won’t allow the engine to be cranked by the wheels’ motion.
Get your car inspected pretrip, and buy a portable jump-starter like Black & Decker’s Start It ($90, amazon.com).