Battery Construction

by the alternator under the lightest of loads (unless you are driving at night in the rain with all the electrical accessories on). While they are great for this “high-power output for a short period of time” application, they are not suitable for use in your EV (other than for powering its accessories) because this battery type has thin plates that are only lightly loaded with active material. Used in an EV, it would give you only the shortest deep-cycle discharge life—you’d be lucky to get 100 cycles out of it. Even on a brief trip, if you stomped down too hard (or for too long) on the accelerator pedal, you’d be lucky to make it back to your own driveway.

Deep-Cycle Batteries

These are what you need. The low end of the capacity range might go into a golf cart–type or low-speed electric vehicle. The upper end of the capacity range goes into your EV. They can also be found in manufacturers’ catalogs under the Marine heading. Any of these are a step up from starting batteries; they have much thicker plates and are specifically designed for a deep-discharge cycle-life in the 400 to 800 cycles (and up) ballpark. Industrial Batteries

These monsters go into forklift pallet and stationary wind- or solar-generation applications. While they give great depth-of-discharge results on paper, have 1,000 cycles and up cycle-life, and make great counterweights for forklifts, their weight and size generally make them unsuitable for EV applications. Your mission is to go after the deep-cycle batteries that might be found under the golf cart, marine, or electric vehicle catalog headings.

Battery Construction

From a manufacturing viewpoint, a lead-acid battery is one of the most efficient things going. While lead is definitely something you don’t want in anything you drink or consume (you don’t even want it in the paint on the wall inside your home), the EPA loves lead-acid batteries because more than 97 percent of these batteries are recycled and 100 percent of every battery is recyclable.

Battery construction makes this possible. Used lead batteries are gathered at collection points, and then sent to smelting specialists where they are disassembled. The lead is melted, refined, and delivered to battery manufacturers and other users; the plastic is ground up and sent to reprocessors who make it into new plastic products; and the acid is collected and either reused or treated.

How a battery is constructed affects which battery you buy. Figure 8-3 shows the details.

Plates

Battery plates are formed on a wire-like grid of lead alloy (antimony is sometimes used to stiffen the lead); a mud-like lead oxide, sulfuric acid, and water paste is applied to them and allowed to harden. An expander is added to the negative cathode plate that prevents it from contracting in use. The plates are then “cooked” in a dilute sulfuric acid solution by sending a forming charge through them that changes the positive anode plate to a highly porous, chocolate-brown lead dioxide material, and changes the negative cathode plate to a gray sponge lead. The positive and negative plates are assembled into a “sandwich” with separators—thin sheets of electrically insulating material that is still porous to the electrolyte—and held in place inside the battery by

Figure 8-3 Lead-acid battery construction.

the plate straps. How thick and heavy these plates are, combined with the efficiency of their design (how much area is exposed), and how efficient the separator is, all collectively determine the capacity of your battery. While the initial way to tell the capacity of a battery is to pick it up, the only real way to tell is by using it.

Case or Container

The case is a plastic or hard rubber one-piece rectangular container with three or six cells molded into it. Each cell has molded-in ribs running across the width of its bottom or down the long dimension of the battery (see Figure 8-3). The plates are mounted at right angles to the ribs, whose multifold purpose is to stiffen the case, support the plates in a non-electrically-conductive manner, and act as collection channels for the active material shed from the plates. A battery is usable until the active material it sheds makes a pile that eventually reaches the plates and shorts them out. All other things being equal, a deeper-case battery will outlive a shallow-case battery because it allows a higher pile of active material to accumulate. Larger industrial batteries are costeffectively rebuilt just by opening them, dumping the used active material, cleaning out any cell residue, and replacing the plates, separators, and electrolyte.

Cell Connectors or Links

These connectors can be inside the battery (through or over the cell partitions) or outside the battery via the link connector (see Figure 8-3). External connectors found in older and larger battery types allow you access to individual cell voltage measurements; improved battery reliability has made individual cell measurements less necessary with modern batteries.

Filler Opening and Vent Plugs

These openings allow you to refill your battery with distilled water or electrolyte solution. Vent plugs are baffled to allow gas to escape but not an accidental electrolyte