Battery Buyer’s Guide
When it comes to your high—performance vehicles, one of the most overlooked upgrades is the battery. While the type of battery under the hood is not going to shave any time off your quarter-mile times (though there are some battery mods that will), getting the best performance from your charging system is always good bet, especially if you have upgraded electronics. This guide will break it down for you so the next time you need to pick up a battery you will know which one to grab and which ones to leave on the shelf.
CA- Cranking Amps, this is the rating of cranking amperage measured at 32 degrees F.
CCA- Cold Cranking Amps, this is the amperage rating the battery can provide at 0-degrees F for 30 seconds without dropping below 7.2 volts. This is the most important measure of a battery, and is the typical rating used for selecting the appropriate battery for a vehicle.
RC- Reserve Capacity, measured in minutes, this is how long the battery will provide 25 amps until the battery voltage drops to 10.5 volts. This is used on both starting and deep cycle batteries.
AH- Amp Hour, typically used for deep-cycle batteries, this illustrates the amperage capacity. A battery with 150 amp hours rating would provide 15 amps for 10 hours, 10 amps for 15 hours or 150 amps for 1 hour.
While most batteries are of the same ages-old lead acid (LA) design, there are many ways to put them together. The main types are Flooded, Gel and AGM (Absorbed Glass Mat). All lead acid batteries use the same overall concept- lead plates (one is lead, the other is lead oxide) are submerged in an electrolyte solution of sulfuric acid. Each of these plate groups is called a cell; a group of individual cells is called a “battery”. As the battery discharges, the lead electrodes become lead sulfate, and the electrolyte dissolves into water. This why batteries freeze during the winter, which can cause the lead plates to touch (short-circuit), effectively destroying the battery. While charging a lead acid battery, through electrolysis, the battery generates oxygen and hydrogen gas, which can be explosive, which is why batteries are typically mounted under the hood, where they dissipate and do not become condensed. When installing a battery in the trunk, a firewall must be installed to protect the passengers; the battery box must also be vented to the exterior of the vehicle.
Flooded- This is the most common type of LA battery but there are couple sub groups- conventional and sealed. Sealed flooded battery are designed to be maintenance—free, meaning you don’t have to add water at any time, they are sealed. A conventional battery, such as a “tar-top” battery in a classic car, each LA cell is separated and each group has its own electrolyte. Over time, the process of charging and discharging uses up the electrolyte and it has to be replaced with distilled water. Some modern batteries still require this kind of maintenance.
Gel- The platform is the same, but instead of using plain old water as the base for the electrolyte, they use a thickened version (like Jell-O) to keep the electrolyte from leaking in the event of a cracked or broken box. This also makes the battery more stable in terms of vibration and installation location, as the gel doesn’t move, which ensures the plates are always covered in electrolyte. One of the drawbacks for gel cell batteries is that they are more susceptible to voltage irregularities and they can’t be refilled, once the electrolyte degrades, the battery is toast.
AGM- AGM or Absorbed Glass Mat batteries are the most efficient of the lead-acid design. AGM batteries use a fiberglass separator to keep the electrolyte between the lead plates. This makes AGM style batteries extremely stable in any position, even upside down. The most famous AGM battery is the Optima brand. Optima batteries use a spiral-wound core with AGM electrolyte seperators, making it impossible for the plates to touch. These batteries last much longer than a conventional or gel-cell battery.
Both gel and AGM batteries degas like flooded batteries, but since they are sealed, the gasses are reabsorbed into the electrolyte, keeping them functional longer. Both types of batteries can release their charge faster than flooded batteries, which is an important function. In order to provide a larger level of cranking amperage, a flooded battery must be much larger, as a typical flooded battery is limited in how much charge it can release at one time. Gel and AGM batteries can release more charge at once. This means that gel cell and AGM batteries can fit in a smaller case while providing more amperage.
There are two sub-classes for all batteries- Starting and Deep-Cycle. Starting batteries, which have higher cranking amps for heavy, short bursts of energy use a larger number of thinner plates to release more amperage. The thinner the plate, the more amps is can release in a burst. The side effect of this is that the plates get hotter faster, which causes them to warp and pit, particularly when they are fully discharged. Deep-cycle batteries use fewer plates, but each plate is thicker, so they store more energy, but can’t release it as fast, only 25% of the rated amperage can be released at one burst. Deep cycle batteries are used for long-term constant draw situations, such as boats, golf carts and show cars (lights and stereo systems). Flooded style deep-cycle batteries should not be used for starting; they do not have the cranking power. AGM deep-cycles, such as the Optima brand, can be successfully used as starting batteries (this is coming from personal experience), in fact, we have used one in an early 70s muscle car, which was daily-driven and used as a car audio demo car for many years, that deep-cycle Optima lasted 5 years with hundreds of full discharges.
New battery designs
There are a couple of newcomers to the automotive battery realms, specifically lithium Ion (Li) and Nickel-Metal Hydride (NiMh). These batteries are commonly used in rechargeable applications for cell phones and other portable devices, they are very stable and hold a charge for a long period of time, with the ability to release that charge quickly. Both types are very efficient, weigh and have a long life, but they are very expensive, a single lithium ion starting battery can cost over $1500.
NiMh- This design uses hydrogen-absorbing alloy as the negative electrode, and nickel oxyhydride as the positive side. NiMh batteries charge fast, but they have a faster discharge rate when idle. These are type of batteries used in hybrid vehicles.
Li- Lithium batteries are very similar to NiMh batteries, but they are slightly more efficient and hold a static charge for longer periods. These batteries are becoming more prevalent in high-performance applications where every pound is critical. Swapping a 40-pound LA battery for a 13-pound Li-ion unit has a definite advantage. In fact, Porsche recently swapped out conventional batteries for Lithium Ion, with a replacement cost of $1700. Using an Li battery in cold weather is not advisable though, as they can be damaged in temperatures below freezing.
Flooded batteries require more maintenance, but all batteries have needs. Lead acid batteries must be charged constantly to maintain that charge. Leaving an LA battery on the shelf for 6 months will degrade the battery, especially if it is in cold weather. You must protect your batteries from freezing, in severe cold weather, a battery can freeze, which will short out the plates and the battery will no longer charge. When a battery freezes, the sides of the box will bulge.
Charging- When storing a battery long term, you should consider a trickle or maintenance charger. These low-amp chargers keep the battery from discharging over time without boiling the electrolyte, which can ruin the battery. There is another side to that coin though. A dead flooded (this does not work for gel or AGM types) battery that won’t hold a charge can sometimes be “jump-started” by boiling the electrolyte with a heavy high-amperage charge. This is because over time and charge/discharge cycles, the electrolyte crystallizes (Sulfation) on the plates. Boiling the electrolyte can re-absorb those crystals, making the battery useful again. This does not work for batteries that have shorted cells. The process for reviving AGM batteries is a little more complex, involving multiple batteries chained together.
Corrosion- Corrosion is a problem with all batteries, moisture, metal and electricity cause electrolysis, the same process at work inside the battery, but in an uncontrolled manner. That fuzzy stuff on your battery terminals is bad. It is the by-product of electrolysis, which is like rust for lead. Preventing it is fairly simple and there are some methods that work better than others. You can buy the felt pads and anti-corrosion spray work, but not for very long. The key here is keeping moisture out while promoting a solid connection to the cables. A little Vaseline on the terminals goes a long way to protect against corrosion. Another solution is liquid electrical tape, which creates an airtight seal, but it has to be cut off before removing the battery cable.
Water level- Flooded batteries require water to function, over time, the water level decreases. While many flooded batteries are labeled “maintenance free”, not all are. You should periodically check the water level in your battery. If the water is below the top of the water holes, add some distilled water. You have to be careful, the water in the battery is highly-corrosive.
Cables and terminals- The battery can only do its job when the connections are good. Corroded cables and terminals, loose fitting terminals, etc limit the alternator’s ability to charge the battery and provide juice to the car. All terminals must fit tight, if you can wiggle it by hand, it’s not tight enough. You have to be careful with side-post terminals, as you can strip the threads and actually break into the case, causing electrolyte to leak out.
Regardless of the type of battery you choose, there will be some decision to be made. A daily-driven econobox doesn’t need a high-performance lithium-ion battery, while a show car needs a battery that can sustain long periods of use without charging. Find the right battery for your needs and it will serve up the juice you need for a long time.