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Battery Myths

SOME OF THE MYTHS ABOUT BATTERIES



If a car is not going to be driven for a several weeks, the battery terminals should be disconnected.

FALSE. Most cars have on-board computers that run the electrics, steering, transmission and security systems. These systems require a continuous amount of power to operate. If you disconnect the battery, you might find that these systems don’t work even when you reconnect the battery. The best way to maintain a battery on extended holidays is to use a maintenance charger. It can be left connected for an indefinite period, ensuring your car battery remains fully charged while you are away.

A battery will not lose its charge sitting in storage.

Depending on the type of battery and temperature, batteries have a natural self-discharge or internal electro chemical "leakage" at a 1% to 25% rate per month. Over time the battery will become sulphated and fully discharged. Higher temperatures accelerate this process. A battery stored at 95°F (35°C) will self-discharge twice as fast than one stored at 75°F (23.9°C).

After leaving the car's lights on and flattening the battery, going for a drive will recharge it

FALSE. You won’t fully recharge your battery by going for a drive, idling the engine, or going for a short stop-start trip. In fact, ‘surface’ charging or continuous undercharging will lower the capacity of the battery over time and shorten its life. You could also void the battery warranty by not recharging it correctly. The only way to reliably restore a flat battery’s charge is to use an appropriate multi-stage battery charger. The charger voltage needs to be high enough to mix the battery acid evenly in the electrolyte to prevent ‘stratification’

The bigger the cold cranking amps (CCA), the better the battery

FALSE. Most cars’ electrical systems are designed around a specific size battery; and the vehicle computer systems regulate the power required for normal operation. Generally, the electrical system will only use a fixed amount of power from the battery based on the requirements of the starter motor and electrical system. A larger CCA battery supplies only what is required. While it won’t damage your car, using batteries with a higher or lower capacity can affect the performance of the car.

Tap water can be used to top up the water level in a battery if the plates are exposed

FALSE. To replace lost water in batteries use distilled, deionised or demineralised water. In an emergency, use rain water from a clean container – this has less impurities than tap water. Tap water can produce mineral build up that blocks the pores and coats the plates of the battery. If the cell plates have been exposed, they can dry out and fail. So, if you’re having to top up water, it’s a good idea to recharge and test the battery at the same time. Note: batteries that have run out of water are not covered under the battery warranty.

Lead-acid batteries have a memory.

Lead-acid batteries do not have the "memory effect" found with first generation Ni-Cad batteries; however, continuous under charging will lower the capacity of the battery. Deep discharges below 10.5 volts can shorten their lives.

Cells in lead-acid batteries will not reverse polarity.

Cell reversal usually occurs when a cell has completely discharged and current is still flowing through the battery. It can be corrected by applying a load, completely the discharging battery, and then recharging the battery with the correct polarity with a low current. The best way to prevent cell reversal from occurring is not to discharge a battery below 10.5 volts or to use a low voltage cut-off.

A battery will not explode.

The two types of battery explosion are external and internal. Recharging a wet lead-acid battery produces hydrogen and oxygen gasses. While spark retarding vent caps help prevent external battery explosions, sparks occur when jumping, connecting or disconnecting charger or battery cables and ignite the gas causing an explosion. Less common internal explosions usually occur while using a deep cycle battery and normally just blow the filler caps or cover off the battery and splatter electrolyte all over the battery box. The most probable cause is from a combination of low electrolyte levels in the battery and a low resistance bridge formed between or across the top of the plates called "treeing" between a positive and negative plate. When current flows in the battery, a spark occurs and ignites the residual gas in one or more of the cells. A second possible cause is a defect in the weld of one of the plate connecting straps. Periodic preventative maintenance, working on batteries in well-ventilated areas, or using sealed AGM or gel cell type batteries can significantly reduce the possibility of battery explosions. To neutralize the residual battery acid, be sure to thoroughly wash the battery box with a solution of one-pound baking soda to one gallon of warm water. The largest number of battery explosions, while starting an engine, occur in hot climates. While not fatal, battery explosions cause thousands of eye and burn injuries each year. Should a battery explosion occur and battery electrolyte (or battery acid) get in someone's eyes, flush them out with any drinkable liquid immediately because SECONDS COUNT.

Pulse chargers, aspirins or additives will revive sulphated batteries.

Using pulse chargers or additives is a very controversial subject. Most battery experts agree that there is no conclusive proof that pulse chargers work any better than constant voltage chargers to remove or prevent sulphation. They also agree that there is no evidence that additives or aspirins provide any long-term benefits. Short term gains maybe achieved by increasing the acidity of the battery but in the long run may harm or reduce the capacity of the battery. The best way to prevent sulphation is to keep the battery fully charged.

Storing a battery on a concrete floor will discharge them.

A hundred years ago when battery cases were made of porous materials such as tar-lined wooden boxes storing batteries on a concrete floor would accelerate their discharge. Modern battery cases are made of polypropylene or hard rubber. These cases seal better, so external leakage-causing discharge is no longer a problem provided the top of the battery is clean. Temperature stratification within very large batteries could accelerate their internal "leakage" or self-discharge if the battery is sitting on an extremely cold floor in a warm room or is installed in a submarine.

Maintenance-free batteries never require maintenance.

In hot climates, the water in the electrolyte is lost due to the high under hood temperatures. Water can also be lost due to excessive charging voltage or charging currents. Non-sealed batteries are recommended in hot climates so distilled water can be added when this occurs.