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Selecting a Battery

By: · August 17, 2009

What’s the best battery? Ask a dozen different experts and you’ll receive a dozen different answers. Some will simply recommend a DieHard. Others swear by immobilized-cell, no-maintenance models. Still others might advocate using the same make and model that’s already in the vehicle in hopes of the battery being covered under warranty…

Battery Basics

Simply put, batteries are energy-storage units that convert chemical energy to electrical energy. This is accomplished when electrons are transferred through an electrolyte within each cell in the battery. The number of cells in the battery determines its output voltage and/or capacity.

Each cell has three main parts: electrodes, separators and the electrolyte. In automotive batteries, metal plates serve as electrodes. Each cell must have at least one positive and one negative electrode; automotive battery cells have multiple pairs. A separator (matted glass material, plastic or simply a space) keeps the positive and negative plates from touching and shorting out.

Ask a dozen different experts and you’ll receive a dozen different answers about the best battery for your vehicle.
Electrons travel between electrodes through the electrolyte. In automotive applications, the electrolyte is commonly known as battery acid. During discharge, the negative plates transfer electrons to an external circuit, such as to the starter motor or headlights. To complete the circuit, the positive plates accept electrons from the alternator, thus recharging the battery.

During charging, the plates give off hydrogen and oxygen. This is known as gassing. To relieve internal pressure, these gasses are vented externally (the corrosion on positive battery posts and battery trays is vented lead oxide). On vented batteries, the accompanying water that’s lost must be replaced to keep the fluid level above the plates. “Maintenance-free” batteries are designed to be gas-resistant via larger electrolyte reservoirs and space-aged alloys added to the lead plates. Less-frequent or even no post-cleaning is a result.

Battery Types

Some specialized batteries immobilize the electrolyte so that the acid won’t leak should the case become damaged. This also allows the battery to be mounting in any position—even upside down.

The two most common methods of immobilizing electrolyte acid is by either adding silica to “gel” the liquid within the cell or using rolled-up mats to absorb the acid and separate the positive and negative plates. Both of these battery styles are maintenance-free and only vent in emergencies in the event of over-pressurization. They typically have less internal resistance than conventional batteries, so they charge faster. Suspended-electrolyte batteries also don’t self-discharge as fast when stored. Trade-offs are that this technology is more expensive, and these batteries are heavier and sometimes offer less reserve capacity (see below) than comparable-size flooded-cell batteries.

Since its invention by Gaston Plante in 1859, the lead-acid battery has been the standard for several reasons. It works in a wide temperature range, materials are affordable and largely recyclable, it doesn’t suffer from battery “memory,” this configuration packs good power output for its size and the lead-acid style has proven reliable for nearly a century and a half.

Lead-acid batteries can be categorized by “job”: standby service, cycle service, and starting/lighting/ignition (SLI, a.k.a. cranking). Standby or “float” batteries provide an uninterrupted secondary power supply, then begin to discharge as soon as the primary (AC) power source is interrupted. One example is a battery-backup system for a computer.

Cycle-service batteries are designed with thick-plate electrodes to serve as primary power sources, to have a constant discharge rate and to repeatedly accept recharging. Also known as “deep cycle” batteries, common cycle-service applications include electric golf carts and boat trolling motors.

SLI batteries are the mainstays for starting internal-combustion engines and powering vehicular accessories. They’re designed to produce high power in short bursts but must be constantly recharged (normally with an alternator while driving). Vehicle starting typically discharges 1%-3% of a healthy SLI battery’s capacity.

Battery Death

According to the Battery Council International (BCI), as many as 85% of the 70 million new lead-acid batteries sold each year will go dead before their approximate 5-year design life. The primary reasons: vibration, lack of maintenance, improper charging and incorrect application.

Vibration can jar a battery’s internals loose. Once the lead plates start to move, they can touch, causing a short. Because a battery is only as good as its worst cell, one loose plate can spoil a whole battery. Many of the more expensive batteries use epoxy paste material to secure the lead plates. These pastes are formulated for the optimal balance between internal resistance (to be as non-intrusive to electron transfer as possible) and durability. These “plate-lock” adhesives can degrade over time, but this technology generally extends battery life compared to units that lack it.

Improper maintenance and charging promote battery failure through sulfation. This is a byproduct of discharging: During discharge, the chemical reaction causes lead sulfate to form on the plates. If the battery isn’t recharged within a few days, the lead sulfate will harden and crystallize, diminishing the battery’s ability to accept a charge. Low water level in the cell will also cause sulfation.

In addition to stimulating sulfation, improper charging damages batteries in other ways. Overcharging causes heat damage and excessive gassing (and can be caused by a faulty alternator/regulator). Undercharging makes a battery more likely to freeze in cold weather.

Routine maintenance will extend battery life. Any corrosion should be cleaned regularly, vent caps should be kept tight, and electrolyte should be kept at the bottom of the splash band. Finally, stored batteries should be kept in a cold location that doesn’t consistently get below 32 degrees F, and their state of charge should be checked every two months.


A standard (maintenance-required) lead-acid battery is designed to produce 100% of its rated capacity at 80 degrees F. Output diminishes to 65% at 32 degrees F and 40% at 0 degrees F. If the battery isn’t fully charged to begin with, capacity suffers even more.

Oil viscosity also affects the battery’s ability to start the engine. If an engine’s cranking-power requirement is 100% at 80 degrees F with 10W-30 oil, that same engine will require 155% of said cranking power at 32 degrees F and 210% at 0 degrees. Using SAE 20 oil, that same engine would need 250%—2 1/2 times—the cranking power to start at 0 degrees F that it would to fire at 80 degrees F with 10W30 oil.

Furthermore, wet-cell batteries can actually freeze at low temperatures. In worst-case scenarios, they become bombs: Their polypropylene cases become icy shells, and the cells emit high-pressure gasses when a charge is introduced. Something has to give. This is why proper jump-start procedures is especially critical in cold weather (see below).


As a pre-emptive strike, buy the freshest battery available. Similar to food’s expiration date, all batteries contain manufacturing-date codes. An honest retailer will help decipher these numbers.

Other warranty questions: Is it nationwide; how long is the free-replacement period; and after the free-replacement period, what’s the prorated-reimbursement policy? On replacement batteries, does the warranty start over again on the date of replacement or extend back to the date of original purchase? Finally, test the battery before embarking on long road trips to minimize the possibility of battery-warranty claims in unfamiliar environs.

Choose The Best

Following the typical American mentality, bigger is better when it comes to batteries. In general, buy the biggest Group Size that will physically fit in the mounting location and the battery model that has the most Cold Cranking Amps and Reserve Capacity you can afford. This reduces the depth of discharge (especially in SLI batteries), extending battery life.

Incidentally, most people make the mistake of shopping on cost alone instead of estimating how many starts the battery will supply per dollar. Also, consult the vehicle’s owner’s manual for its minimum-rating battery recommendation.

AC-Delco devised a more scientific approach for determining CCA requirements. Their rule of thumb is to multiply engine displacement in cubic inches by 1.5. So, a Chevy 350 should have a minimum 525 CCA battery; realistically more in cold country. (Batteries rated solely in CCA should only be used for SLI applications.)

Battery style depends on the application, and each style has certain inherent compromises. The best battery for your vehicle is the one that offers the fewest drawbacks. Here are a few guidelines.

Flooded-Cell Maintenance SLI—Positives: Lowest initial cost, adequate for many commuter cars and for mounting locations that allow easy access, hands-on owners can monitor battery’s “health” by checking the electrolyte’s specific gravity with a hydrometer.

Negatives: Water level must be monitored at least once a year (more often in hot climates); cells should be filled with distilled water to minimize internal resistance, and overfilling with water can cause acid to spill out the vent caps. These batteries shouldn’t be used for non-starting applications (powering electrical accessories while the engine isn’t running)/must not be deeply discharged and should be recharged soon after discharge. Likely applications: Commuter cars owned by people who don’t mind dirt under their fingernails.

Flooded-Cell Maintenance-Free SLI—Positives: Doesn’t require attention until it dies, satisfactory for starting duties in most frequently used vehicles.

Negatives: “Charge level eyes” are notoriously inaccurate, self-discharge more rapidly than most other styles when not used. Likely applications: Cars whose owners loathe looking under the hood.

Immobilized-Electrolyte SLI—Positives: No maintenance, can operate in any position, have a long shelf life, have a low rate of self-discharge, so they typically last two to three times as long as flooded-cell units. (Optima reports Society of Automotive Engineers life-cycle testing as 12,000 starts for its 800 CCA red-top battery versus 4,000 starts for conventional batteries.)

Negatives: Initially more expensive than flooded-cell batteries, sensitive to overcharging (check alternator/regulator for proper voltage), shouldn’t be allowed to self-discharge below 11.5 volts, gel-cell styles often have higher internal resistance and sometimes can’t transfer current as efficiently as other styles. Likely applications: High-vibration environments such as off-road vehicles and/or where battery corrosion is a concern (such as collector/show cars).

Flooded-Cell Deep-Cycle—Positives: Can deliver full capacity through multiple charge cycles, can be significantly discharged without causing damage, can be left in a discharged state longer than SLIs. Negatives: Discharging below 50% of capacity shortens life, many models don’t have enough CCA for starting duties, self-discharge and sulfation can occur if neglected for long periods during storage, best when used in multiples to reduce discharge level to each individual battery. Likely applications: As a power source for auxiliary accessories, such as vehicle-mounted winches and high-watt audio systems; many marine and RV uses.

Immobilized-Electrolyte Deep-Cycle—Positives: Same as above, no maintenance, can be mounted in any position, rate of self-discharge is less than flooded-cell units (although batteries can lose up to 1% of capacity per day when left uncharged), some models have enough CCA to be used for SLI duties. Negatives: Expensive, state of “health” requires a voltmeter to monitor. Likely applications: Possibly the best all-around choice: some models can function as dual-purpose cranking/deep-cycle batteries, good for vehicles whose auxiliary power requirements (winches, lights, mega-watt sound system, etc.) exceed the alternator’s charging capability and/or run accessories with the engine off.

Battery Safety

Battery acid, or electrolyte, is a solution of sulfuric acid and water. Most people are aware that battery acid eats through clothing and burns skin. When handling flooded-cell batteries, use caution and keep an acid neutralizer such as baking soda or household ammonia mixed with water nearby. Follow these wet-cell handling tips: Wear eye, face and hand protection. If battery acid contacts the eye, hold the eyelids open and flush the eyeball with clean, cool water for at least 15 minutes and seek medical attention. If battery acid is swallowed, drink lots of water or milk. Don’t induce vomiting and seek medical help immediately. Finally, neutralize any spills with baking soda, then rinse the affected area with water.


These days, many people call the Auto Club when they need a jump. However, portable jump-start units are becoming increasingly popular, so here’s a primer on proper technique.

Wear eye protection and never lean over the dead battery in case it gasses. Inspect both batteries for signs of case damage before jumping. Don’t connect jumper cables to any battery that appears damaged. On maintenance-required batteries, make sure that the vent caps are tightly seated. Make certain that the vehicles are not touching and both ignition switches are turned to the OFF position. Refer to the vehicle owners’ manual, particularly on late-model vehicles that have advanced electronic features. Unplug any cigarette-lighter-powered accessories such as cell phone chargers, laptop computers and radar detectors, which may be damaged by voltage spikes.

The Jumping Sequence—1.) Connect the positive/red (+) jumper cable to the positive (+) terminal of the discharged battery. 2.) Connect the other end of the positive/red (+) cable to the positive (+) terminal of the charged battery. 3.) Connect the negative/black (-) cable to the negative (-) terminal of the charged battery. 4.) Connect the other end of the negative/black (-) cable to non-painted metal that’s away from the battery, such as the alternator mounting bracket. DO NOT connect the negative/black (-) cable to the negative (-) post on the discharged battery—this can cause a defective battery to explode. 5.) Start the dead vehicle and remove the cables in the reverse order of the connections, taking care not to touch the cables’ clamps together until all are disconnected.

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