Everything You Need to Know About Car Batteries

Engine Start/Stop button

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The internal combustion engine has been around for well over a century, the first engines put to use in the late 1860s, but starting them wasn’t as easy as turning an ignition key or pressing the start-stop button. In those days, starting was done by a hand crank, which would give the engine enough compression to fire off a cylinder. The flywheel might carry it over to the next firing, or it might not, at which the operator would have to crank the engine again.

Early drivers didn’t crank their engines for long, however, with car batteries and electric starters available as early as 1911. The first airplanes were, quite dangerously, started by hand until 1930, requiring someone to turn the propeller. The introduction of the electric starter made it possible to start ever larger and more powerful engines, which would be impossible to crank by hand, but without car batteries, even electric starters would have no way to energize.

Today, all piston-driven internal combustion engines are equipped with car batteries and electric starters. The car battery is designed only to supply a short burst of high power, just enough to move the engine a couple-hundred rpm. Once the engine starts, the electric starter disengages, having drained a few percentage points off the car battery’s state of charge (SOC).

All vehicle electrical systems require power, including the ignition and fuel system, engine and transmission controls, audio and climate control, to name a few, but the car battery isn’t designed to power these for very long. In fact, it might last only a few minutes, and ruin itself at the same time. With the engine running, the generator, also called an alternator, kicks in to generate electricity for the rest of the vehicle, usually between 13.5 V and 14.5 V. This is enough power to run the vehicle and keep the battery charged.

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How Car Batteries Are Made

1953 Car Battery illustration

National Institute of Standards and Technology/Wikimedia Commons/Public Domain

Car batteries are energy storage devices, storing their energy in chemical form. The most common, fairly bulletproof technology — not actually bulletproof — is the flooded lead-acid battery. Alternating plates of lead, the anode, and lead oxide, the cathode, are submerged in a bath of sulfuric acid electrolyte, or “battery acid.” Each cell holds 2.1 V, and car batteries are made of six cells, so the typical “12 V” car battery holds 12.6 V at full SOC. Less common AGM (absorbed glass mat) car batteries also use six lead-acid cells, not a liquid electrolyte, but a gel electrolyte trapped in fiberglass mats.

With the introduction of hybrid and electric vehicles, car batteries are changing. Hybrid and electric vehicle batteries look nothing like 12 V batteries and probably aren’t even visible or accessible by the typical driver or DIYer. Packing upwards of 300 V, these car batteries can kill an unprotected person. Fortunately, these batteries are well-protected and well-hidden from unpracticed hands.

Hybrid vehicles may still use a small 12 V pony battery to operate vehicle electrical systems, but engine starting and running power is provided by the main battery pack and voltage converters. Hybrid car batteries are typically NiMH or Li-ion (nickel-metal hydride or lithium-ion).

Electric car batteries are almost universally Li-ion, which is more energy-dense than NiMH, important for space, weight, and range considerations, but may still use a small 12 V pony battery for electronics when the vehicle is not “running.” When running, voltage converters power vehicle electronics and recharge the 12 V battery.

Ongoing car battery research has gone into other chemistries, such as LiFePO4 and LisO2 (lithium-iron phosphate and lithium-sulfur dioxide), or supercapacitor technology, which charge and discharge nearly instantaneously.

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How to Care for Car Batteries

Crash test dummy jump starting a car

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There are three main ways to kill car batteries: heat, vibration, and discharging.

  • Heat accelerates corrosion and electrolyte evaporation, both of which can kill a car battery. If the battery has air dams or tubes to direct air at or around it, removal could prevent proper cooling.
  • Vibration shakes the plates around and can loosen internal connections. A properly fitted battery hold-down will prevent excessive vibration from ruining the battery.
  • Discharging is the absolute worst thing for a lead-acid battery, meant only for short bursts of high power. Plate sulfation impacts battery SOH (state of health), and can occur in a discharged battery. Leaving the lights on overnight or leaving things plugged in all day might require a jump start, but the battery will never fully recover.
  • Short trips will also kill a car battery, as the generator isn’t running long enough to fully charge the battery every time the car is started. A float charger or battery maintainer is a good idea for those who don’t take long trips.
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The Battery Life Cycle

Car battery landfill

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Today’s car batteries typically last 4 to 7 years, depending on climate, use, and care. Today’s battery testing methods have improved significantly, but a failing car battery will give you warning signs, such as dimmer headlights, strange air conditioning compressor noises, or slow engine cranking. Have the car battery tested regularly, especially before Winter, which can kill a weak battery.

Replacing car batteries is an easy job, requiring just a couple basic hand tools. Start by disconnecting the battery negative terminal, usually marked in black or with a (–) symbol. Then disconnect the battery positive terminal, usually marked in red or with a (+) symbol. Remove the battery hold-down and the battery. Clean corrosion from the battery cables, then install the battery in the reverse order of removal.

Once you’ve removed your old car battery, bring it to a recycling station or transfer station — the autoparts store usually will take it back when you buy a new battery. Car battery recycling keeps dangerous chemicals and elements from getting into the environment. Used lead plates are recycled into dozens of other products, as is the sulfuric acid electrolyte and even plastic casings, often back into new car batteries.

Car batteries start our cars and trucks, in all seasons and all weather, and taking care of them keeps them keeping us on the move for years at a time.