Battery packs are used to jump start stalled engines and can also serve as a general purpose emergency power supply. Here’s how to choose a reliable jump starter. We look at rechargeable 12V automotive battery packs.
Anyone can forget to switch the car lights off and cause the battery to go flat.
An emergency jump starter pack or battery booster, allows drivers to start their own car without having to flag down passing motorists or call a mechanic for help. This is safer, cheaper and more reliable. Especially late at night, on deserted roads or in the middle of winter.
The jump starter can also be used as an alternative to a backup generator: for disaster preparedness, camping, tailgating or to run power tools through an inverter (instead of using cordless tools).
Jump starters use rechargeable 12 volt lead-acid batteries just like a regular car battery (though they use smaller batteries). They weigh between 20 to 30 pounds and cost from $70 to over $100. Warranties are typically 2 years. Popular brands include Everstart, Black & Decker (Simple Start), Duracell, Husky, Schumacher, Duralast, Endurance and Vector.
“Battery booster” can mean an emergency charger or a jump starter. A charger is not a jump starter. The difference is explained below.
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Jump Starter Power and Amps
It takes a lot of power or current to start a car engine. Standard jump starters can start 4-cylinder cars. Trucks and V8s need more powerful jump starters. Jump starters are rated based on peak amps and cranking amps (or just amps). It is important to not confuse the two when comparing jump starters.
- Cranking amps are usually a few hundred amps. They should be at least as high as the cold crank amps (CCA) specified by the car’s manufacturer.
- Peak amps are a few times higher than cranking amps. Some jump starters are rated to over 1000 peak amps. Peak amps are less useful as they aren’t usually specified by the automobile manufacturer, so there is nothing to compare them with.
The capacity of the battery determines how many times it can jump start before it needs to be recharged. Most batteries can store 14 to 28 ampere-hours of electricity: enough for a few jump starts.
Jump Starter Features
The most important feature is the ability to jump start a completely flat battery. Some jump starters can work with a weak battery but not a completely discharged battery.
A polarity reversal alarm is useful, warning when the jumper cables are connected wrongly. However depending on the design, the same safety mechanism can shut off the jump starter when it is connected to a flat battery (cannot recharge flat batteries). A safety versus versatility trade-off is involved.
Other useful features include:
- Charging through household AC mains socket.
- Charging through the car’s cigarette lighter socket.
- Overcharge protection, allowing the jump starter to be conveniently left plugged-in without damaging the battery.
- Over discharge protection.
- Remaining charge indicator.
- Replaceable battery.
- Ability to connect a second battery to increase available capacity (not for jump-starting, for use as an emergency power supply).
A 12 volt cigarette lighter socket is a standard feature, allowing standard car accessories to be plugged in. The following additional features are useful but can be purchased and plugged in separately into the cigarette lighter socket:
- 5 volt USB socket.
- 120 volt AC inverter.
- Radio (good for disaster preparedness).
- Air compressor (tire inflator). These are usually noisy and slow but are better than nothing.
Cigarette Lighter Emergency Battery Chargers
Emergency chargers are low-current battery packs. They charge the car’s battery through the cigarette lighter socket.
- No need to open up the hood and fiddle with jumper cables: useful in rain, snow or high-crime neighborhoods.
- Not possible to connect the wrong jumper cable.
- Not as reliable as a jump starter. Usually underpowered, can recharge a slightly discharged battery but not a flat battery.
- Can take 10 to 30 minutes to charge.
Some chargers are small: 2 to 3 pounds with a 1 or 2 amp-hour capacity. This makes them barely powerful enough to be useful. Some are single-use disposable devices. More powerful chargers are built like jump starters: heavy and using a rechargeable lead-acid battery.
Any battery pack that delivers power through the cigarette lighter socket is a charger, not a jump starter, no matter what the manufacturer says. The cigarette lighter circuit is too light to handle the hundreds of amps needed for a jump start.
The Best Emergency Car Battery Jump Starter
Emergency jump starters are useful but do require some maintenance. They aren’t “buy and forget.” They should be:
- Specified by the manufacturer as being able to jump start a car with a completely flat battery.
- Rated at least as high as the car’s cold crank amps.
- Rated to store at least 10 amp-hours of charge.
- Recharged every month.
- Regularly tested with a medium power appliance (table fan, small TV) through a DC to AC inverter.
- Protected against high and low temperatures. They typically need to be stored between 32 to 104 degrees Fahrenheit and can’t be left to freeze or bake in the car trunk.
To monitor the car’s battery to guard against premature failure, a battery tester should be used. Car owners should also read Bill Darden’s excellent Car and Deep Cycle Battery FAQ (http://jgdarden.com/batteryfaq/carfaq.htm). Some of the information in this article is based on user reviews of jump starters on the Amazon.com website.