Battery Inspection and Sales

Yes, it’s that time of year again, when more and more vehicles are being towed because the charging system failed.

The poor batteries have been pushed to their limit by Old Man Winter. Hard starting, especially in cold conditions, can often be prevented if proper preventative maintenance is followed. Just checking the open voltage of the car’s battery is not enough to know if the electrical system is okay. A proper evaluation of the entire charging system should start with the inspection of the alternator belt, then visually inspecting the system for any broken wires or signs of corrosion.

Inspection and Recharging

Typically, a fully charged battery is 12.6 volts. It has six cells, with each fully charged cell generating 2.1 volts. Checking the specific gravity of the electrolyte of each cell can determine the charge status of the battery. Specific gravity of a fully charged cell is 1.265 and can be checked using a hydrometer or, more accurately, a refractometer. The table shows the state of charge of a battery, the specific gravity, and the voltage.

To find the voltage of each cell of the battery using only the specific gravity, you can use the “84 rule.” The voltage of the cell can be obtained by simply adding 0.84 to the specific gravity reading from that cell. To find the voltage for the entire battery, add all the results together.

Before charging a battery, always determine what type of battery you are dealing with. The procedure for charging a regular (wet cell) lead acid battery is different from the proce-dures for charging gel cell and glass mat type batteries. These batteries are more sensitive and must be charged at a slower rate. If an attempt is made to charge them too quickly, the high amperage can cause them to overheat, and this will shorten their life. A typical charge rate for the gel cell and glass mat battery is about 3 amps at no more than 13.5 to 14.0 volts.

A perfect battery with no load will have no internal current flow, but it will have potential energy. This current flow within the battery is called leakage current and is undesirable. This is why battery manufacturers are trying to minimize it.

Assuming conventional current flow, when the battery is being discharged and therefore supplying the current, the current flows from the battery’s positive terminal through the load to the negative terminal.

Charging System and Battery Limitations

When the battery is being recharged, the generator supplies the current. The current flows from the generator’s positive terminal, through the battery, back to the generator’s negative terminal. This is due to the generator having a higher voltage potential than the battery.

A regular automotive battery is not a deep-cycle battery and must never be treated like one. Operating the stereo or leaving the lights on for long periods, without the engine running, drains the power from the battery. Every time this happens, the plates inside the battery break down.

The process is like breaking a piece of bread: there are always crumbs. These pieces of material that shed from the plates cause the plate’s surface area to be decreased, which means there will be less electron flow, and therefore a shorter battery life. One other major problem that can occur when the plates are broken down is a dead short in the battery’s internal circuit. This happens when the materials that break off the plate get trapped between two plates, creating a short circuit.

A deep-cycle battery is able to withstand this breaking down of the plates when its power is drained down continuously without recharging, as a deep-cycle battery has thicker plates, making them stronger and less susceptible to plate degradation.

Also, thicker plates mean more surface area that, in turn, results in a greater amount of electron flow for a longer period of time before becoming fully discharged.

Gel cell and glass mat batteries can withstand deep cycling better than a regular (wet cell) lead acid battery because of their plate design.

The plates of these batteries are spiral-shaped, so more plates can be packed into a smaller area. More plates mean more surface area for electron flow, resulting in more power for a longer period of time before the battery is discharged.

Also, due to their spiral design, the plates are spaced closer to each other thus dramatically lowering the battery’s internal resistance.

Selecting the right battery for a customer’s needs is vital. When selecting a battery, they should be advised to keep two things in mind: always get a battery with the proper dimensions for the battery tray, and also get a battery with the highest cold cranking amps possible.

One other important factor is to ensure that the battery is not excessively old; the longer the battery sits on the shelf, the shorter its life will be. Each battery carries an identification sticker. On that sticker there will be a letter and a number together. The letter represents the year and the number represents the month the battery was built. Typically, January is represented by the letter A, February B and so on.

With all the complex electronics that are found on the modern vehicle, the battery and charging system are constantly being extended to their limits. Thus, it is necessary to maintain the electrical system for optimum vehicle performance.

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Glenville Singh is with the Canadian Automotive Repair and Service Council. For more information on automotive technology visit CARS OnDemand training at: www.cars-council.ca.