Equipment Type

How to Choose Batteries

Battery Basics 101 identifies two types of batteries: engine start and deep cycle. Typically, engine start batteries have shallow discharge. For instance, when you start your car, the battery discharge is 1 percent or less. But if you have a lot of auxiliary power on that vehicle, say, a police cruiser with its flashing lights and computers, the extra demand for power drains the battery. Engine start batteries won’t last long in that application.

August 01, 2007
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Battery Basics 101 identifies two types of batteries: engine start and deep cycle. Typically, engine-start batteries have shallow discharge. For instance, when you start your car, the battery discharge is 1 percent or less. But if you have a lotof auxiliary power on that vehicle, say, a police cruiser with its flashing lights and computers, the extra demand for power drains the battery. Engine-start batteries won't last long in that application.

A deep-cycle battery that discharges 5 percent, 10 percent, or even more of the battery's capability will handle that extra power demand.

Deciding which type you need is standard operating procedure for most fleet managers, but where the trail divides and where more consideration is needed than there used to be, is in battery design itself. Although there are some "gel cell" electrolyte batteries out there, they are used for such applications as wheel chairs and lawn mowers. The major performers are two basic designs: AGM (absorbed glass mat) and conventional flooded, or wet, batteries.

Flooded batteries have long dominated the market and they still do, but improved technology and availability of AGM batteries are presenting fleet professionals today with a second choice.

Although it is a relative newcomer to fleet operations, AGM technology has been around for 40 years, according to Ronald Rizzo, director of applications and sales engineering for Optima Batteries, a private label of Johnson Control.

"AGM was first used in small sizes, 1 to 30 amp hours, for such applications as back-up batteries for cash registers and to power flashing lights on highway barricades," he says. However, today it is gaining wider acceptance among fleets because some of the early misgivings have been disproved, according to Rizzo.

Several factors caused delayed acceptance of AGM batteries in fleet operations, says Rizzo. First of all, not every battery manufacturer makes them because they are more difficult to manufacture than traditional wet batteries. Early on, he says, that contributed to an availability issue. Also, AGM batteries are more expensive than flooded batteries, so many fleet managers shied away from them for budgetary reasons.

The upside of AGM is that they last longer; they resist vibration better than other types, which is a plus in the often hostile off-road environment; they can be mounted almost anywhere, and fleet managers don't have to worry about corrosion on cables or posts, according to Rizzo."The fleet guy is faced with two big issues when it comes to the battery," he says. "The batteries either are not held down properly or, two, the cables aren't as tight as they should be, probably because of all the bouncing around. If you have a loose cable connection and you get water in there, it's possible you could get corrosion, but we haven't seen any."

With a wet battery, says Rizzo, (Johnson Control manufactures both types) if acid vibrates out and goes along the case, getting to the post and connectors, "you will have a nice surface build up."

AGM batteries also maintain their power capability, Rizzo says. "They keep their electrical performance, or capacity, longer. If the battery has been out there for a few years, it won't be able to perform at the same level as it did when it was new. AGM tends to hold up its voltage level better than traditional wet batteries."

The start-zone power of the battery is another important area, he says, defining it as start capability of the battery in the first 10 seconds of cranking. "These days, especially with cars, if the engine doesn't start within three to five seconds, there is probably something else wrong, not the battery."

Many of the vehicles in a construction fleet are powered by diesel engines, and diesels require batteries that have a high cranking current, especially under low-temperature conditions, Rizzo says.

AGM battery construction plays a role in all this, according to Rizzo. "A wet battery has a polyethylene envelope that wraps around the plates. AGM is made out of 100-percent glass fiber that is very porous and is placed between the plates. Both types act as dividers that separate the positive and negative plates so they don't short out."

The difference is in the separator. "AGM is very porous and holds a lot of electrolyte," Rizzo says. "If you cut open an AGM battery, you will find there is no liquid in it. You might see a drop or two of condensation, but all the acid is tied up in the pores and in the active material plates and in the separator. By comparison, if you cut open a flooded battery, or wet battery, you'll find about a gallon of liquid in there."

As many advantages as AGM has, there is not general wide-spread acceptance. "We make 110 million batteries globally each year, and AGM is a small percentage of that," he says. "The world still uses wet batteries for the most part because people don't want to pay the increased price of the AGM battery."

Dry-cell-battery design is about two- to two-and-a-half times the cost of flooded batteries, according to John Connell, director of sales and marketing for Crown Battery, who primarily makes flooded batteries.

"All fleet managers look for three basic things in a battery," says Connell. "They want quality, service and price. Fleet applications today are becoming extremely challenging as it affects battery application. There is a real need for batteries that can hold up to the power requirements of every day, heavy-duty equipment.

"I would suggest that there is a major problem out there with premature battery failure due to extreme electrical demand imposed upon the battery. If fleet managers aren't careful," he says, "they might not get a proper return on their battery investment."

The problem isn't necessarily that of the fleet professional, says Connell. "Today, OEMs are adding a great deal of electrical load, or more power requirements, on new equipment. Ultimately, when you get down to it, they are relying on the battery or batteries in those machines to supply a greater percentage of that load. Machine designs have evolved beyond the point where conventional battery technology can make up the difference. Fleet managers have to understand that in making a purchasing decision."

In fact, one of the biggest mistakes a fleet manager makes when it comes to buying batteries is basing the replacement cost of a battery on price rather than on the actual power requirement, or service requirement, of the application, Connell says. This is why flooded batteries are the most prevalent in the marketplace, Connell says: They are the most cost-justified and the most proven.

Flooded batteries consist of a positive and negative plate that are submerged in electrolyte. This combination of plates and electrolyte creates a chemical reaction that allows the battery to store, and on demand, deliver electrical current to the machine. "Flooded batteries are electrochemical storage devices that rely on flooded design," Connell says.

Too often, fleet managers assume that one battery is as good as another, says Connell. However, there are major differences in the construction and performance that make big differences when they are in the application, he says.

"Batteries that weigh more deliver more. They contain greater amounts of active lead material and, therefore, they will deliver stronger electrical current in terms of on-demand loads imposed on the battery."

He says batteries that utilize more lead perform stronger and have longer service life. "Battery weight is the equalizer. It is what separates batteries in terms of rating capacity on paper and in terms of actual performance in the field."

Although batteries used throughout construction fleets are considered "maintenance free," says Connell, all that means traditionally is that the fleet manager doesn't have to open up the battery to refill it with fluid.

"By virtue of their design, maintenance-free batteries provide the benefit of not losing fluid throughout their service life," Connell says. "But it does not mean that fleet managers do not have to periodically maintain the product. Terminals must be cleaned from corrosion. Batteries must be inspected for state-of-charge and for capacity. Also,cable connections must be inspected to make sure they are not corroded."

Although it depends on the fleet manager's operation, battery inspections should take place every 15,000 to 20,000 miles, says Connell.

Rizzo says "maintenance-free" AGM batteries are pretty much that. "You install the battery and go. With Optima, you can't add water to it, and you don't want to try and pry it open. There is no accessibility to individual cells. It is completely sealed and has a venting system in it. If it ever gets into an overcharged situation and it has to vent, it will do that, re-seal, and still be operational."

The two see bright futures for each battery design. All said, the final decision is still up to the individual fleet manager and his perception of which technology is right for his operation.

 
 

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