A car battery is a rechargeable electrochemical device that stores chemical energy and releases it as electrical energy upon demand. The battery stores chemicals not electricity.

Lead-acid batteries are used for a vast number of purposes, but all batteries provide either starting or deep cycle power. The only difference is how much power is delivered and how long it needs to be delivered.

Type of Lead-Acid Battery

Starting Batteries
These batteries start engines on cars, boats and other vehicles. They provide a short burst of strong power to get the engine started.

Deep Cycle
These batteries power electrical accessories, such as lights, trolling motors or winches. They provide a low, but steady level of power for a longer period of time than a starting battery.

Deep Cycle – Consumer
These batteries are small, six-volt, deep cycle batteries. They power consumer products and tools like drills, flashlights, electric starters for gas lawn mowers, and children’s toy cars.

Deep Cycle – Industrial
These batteries, used for industrial purposes, take a deep cycle battery further. They provide low, steady power over a much longer period of time than a typical deep cycle battery. The plates are much thicker, and there is usually much more total energy available for a longer period of time. An industrial battery lasts for years.

Function of an automotive battery:
SLI – Starting, Lighting and Ignition

  • Supplies power to the starter and ignition system to start the engine.
  • Supplies the extra power necessary when the vehicle’s electrical load exceeds the supply from the charging system.
  • Supplies power to accessories when engine is off.
  • Acts as a voltage stabilizer in the electrical system. The battery evens out voltage spikes and prevents them from damaging other components in the electrical system.

Function of a standby battery:

  • They supply emergency power when the main power source has failed for any reasons.
  • They are kept fully charged so that they can “kick in” immediately.
  • The batteries remain connected to a trickle charger that will keep the battery fully charged and ready for use.

How a battery is made:

Batteries are made of seven basic components

  1. A resilient plastic container & cover.
  2. Positive and negative internal plates made of lead.
  3. Plate separators made of porous synthetic material.
  4. Electrolyte, a dilute solution of sulfuric acid and water better known as battery acid.
  5. Lead terminals, the connection point between the battery and whatever it powers.
  6. Inter Cell Connectors. Connect one cell to the other in series.
  7. Vent & Vent Caps.

How does a battery work?

A battery stores electricity for future use. It develops voltage from the chemical reaction produced when two unlike materials, such as the positive and negative plates, are immersed in the electrolyte.

In a typical lead-acid battery, the voltage is approximately 2.11 volts per cell, for a total of 12 volts.

Lead-acid batteries operate in a constant process of charge and discharge. Current flows from the battery when battery is connected to a load that needs electricity such as the starter in your car. The battery begins to be discharged.

The basic Chemical reaction that takes place during discharging: The sulfate of Sulfuric acid combined with lead on plate’s active material leaving weaker acid solution. Hydrogen of acid and oxygen of lead peroxide combine to form water, diluting solution.

In the reverse process, a battery becomes charged when current flows back into it, restoring the chemical difference between the plates. This happens when you’re driving without any accessories and the alternator puts current back into the battery.

Battery Capacity

Starting Power is known as Cold Cranking Amps (CCA)
The total surface area of the plates exposed to the battery acid and the rate of diffusion determines a battery potential power. A standardized system (CCA) was developed to have a true comparison of starting power between batteries.

The standardized measure of a battery’s capacity to provide power to accessories is called Reserve Capacity.

Deep Cycle Batteries also have an alternative measure of a battery’s capacity to provide power for accessories called amp hours.

Battery Capacity Definition

COLD CRANKING AMPS – CCA is the current in amperes that a new fully charged battery (at -ISC) can deliver for 30 seconds and maintain a terminal voltage (under load) of L2 volts per cell or more, (7.2 volts for a 12 volt battery). In short, the higher the CCA rating, the higher the battery’s engine-cranking ability.

RESERVE CAPACITY – RC is the time in MINUTES that a new, fully charged battery at 25°C will deliver 25 amperes down to a terminal voltage (under load) of 1.75 volts per cell (10.5 volts for a 12-volts battery). In short, how many minutes a battery can supply the electrical load of vehicle once the charging system has failed.

AMP HOUR CAPACITY – AH is the current that a new, fully charged battery at 25°C will deliver over a period of 20 hours down to a terminal voltage (under load) of 1.75 volts per cell, expressed as amp hour. Simply put the current or amps a battery can deliver continuously over 20 hours. This rating is normally used for deep cycle batteries.

Battery Test & Diagnostics

Causes of Battery Failure

Overcharging is the biggest killer of batteries. Excessive current produces heat which expands and breaks the grid causing the plate to short with each other and the active material to fall off from the plate resulting to premature battery failure. Heat from overcharging also caused evaporation of water in the electrolyte causing the cell to prematurely dry up.

Close second is undercharging. Batteries left unused and discharged for extended period will cause plates to harden and sulphate. Regular short trips (stop/start situation) will also create same problem because more power is taken out from the battery than what is being put in.

Battery not held properly in the cradle will vibrate and jump while the vehicle is moving, causing the active material on the plate to fall off resulting to lose of power and battery to fail.

Corrosion between battery post and cable also put strain on the battery. This corrosion limits the current flow to the battery during charging and severely hampers power from battery during starting.

In cold climates, normally a battery “ages” as the active positive plate material sheds (or flakes off) due to the expansion and contraction that occurs during the discharge and recharge cycles. Brown sediment, called sludge or “mud/’ builds up in the bottom of the case and can short the cell out. In hot climates, additional causes of failure are positive grid growth, negative grid shrinkage, buckling of plates, or loss of water.

Another major cause of premature battery failure is lead sulphation. Using tap refill batteries can produce calcium sulfate that also will coat the plates and fill the pores. Recharging a sulphated battery is like trying to wash your hands with gloves on. When the active material in the plates can no longer sustain a discharge current, the battery “dies”.

Battery Preventive Maintenance

  1. Maintain correct electrolyte level – add only distilled water to within 1/8 to 1/4 inch (3 to 7 mm) below the bottom of the filler tube (vent wells or splash barrel). The plates need to be covered with electrolyte at all times. Avoid over- filling especially in hot climates, because heat causes the electrolyte to expand and overflow.
  2. Remove corrosion from both ends of each battery cable and both terminals.
  3. Clean the battery top.
  4. Check the alternator belt tension.
  5. Check battery hold-down.

The preventive maintenance frequency is dependent upon climate and battery type, but you should perform this at least once before cold weather starts and once a month in warm weather.

Battery Testing



Battery Testing


Visually inspect for obvious problems: loose or broken alternator belt, electrolyte levels below the top of the plates, dirty battery top, corroded or swollen cables, corroded terminal clamps, loose hold-down clamps, loose cable terminals, or a leaking or damaged battery case.

If the electrolyte levels are low in non-sealed batteries, allow the battery to cool and add distilled water to between 1/8 to 1/4 inch (3 to 7 mm) below the bottom of the plastic filler tube (vent wells).


Recharge the battery to 100% State-of-Charge. If the battery has a difference of 0.03 specific gravity reading between the lowest and highest cell, then you should equalize it.

To equalize, increase the charging voltage, add 5%. Heavy gassing should start occurring. Take specific gravity readings in each cell once per hour. Equalization has occurred once the specific gravity values no longer rise during the gassing stage.


Surface charge is the uneven mixture of sulfuric acid and water along the surface of the plates as a result of charging or discharging. It will make a weak battery appear good or a good battery appears bad. You need to eliminate the surface charge by one of the following methods

  1. Allow the battery to sit for between four to twelve hours to allow for the surface charge to dissipate, or
  2. Turn the headlights on high beam for five minutes, shut them off, and wait five to ten minutes, or
  3. With a battery load tester, apply a load at one-half the battery’s CCA rating for 15 seconds and then wait five to ten minutes.


If the battery’s electrolyte is above 110° F (43.3°C)? Allow it to cool. To determine the battery’s State-of-Charge with the battery’s electrolyte temperature at 80° F (26.7°C), use the following table, which assumes that 1.265 specific gravity reading is a fully charged battery:

Battery Testing – Measure the State-of-Charge

If you are using a non-temperature compensated HYDROMETER, make the adjustments indicated in the table to follow. For example, at 30° F (-1.10°C), the specific gravity reading would be 1.245 for a 100% State-of-Charge, testing the same battery at 100° F (37.8°C), the specific gravity would be 1.273 for 100% State-of- Charge.

If you are using a DIGITAL VOLTMETER, also make the adjustments indicated in the following table. For example, at 30° F (-1.1°C)? The voltage reading would be 12.53 for a 100% State-of-Charge, same battery tested at 100° F (37.8°C) 5 the voltage would be 12.698 for 100% State-of-Charge.

Battery Testing – Measure the State-of-Charge

For non-sealed batteries, check the specific gravity in each cell with a hydrometer and average the readings. For sealed batteries, measure the Open Circuit Voltage across the battery terminals with an accurate digital voltmeter. This is the only way you can determine the State-of-Charge. Some batteries have a built-in hydrometer, which only measures the State-of-Charge in ONE of its six cells.

If the built-in indicator is clear or light yellow, then the battery has a low electrolyte level and should be refilled and recharged before proceeding. If sealed, the battery is toast and should be replaced. If the State-of-Charge is BELOW 75% using either the specific gravity or voltage test or the built-in hydrometer indicates “bad” (usually dark), then the battery needs to be recharged BEFORE proceeding.

Battery Testing – Measure the State-of-Charge

  1. If there is a .050 (sometimes expressed as 50 “points”) or more difference in the specific gravity reading between the highest and lowest cell, you have a weak or dead cell(s).
  2. If the battery will not recharge to a 75% or more State-of-Charge level or if the built-in hydrometer still does not indicate “good” (usually green, which indicates a 65% State-of- Charge or better), buy a new one.
  3. If a digital voltmeter indicates 0 volts, you have an open cell.
  4. If the digital voltmeter indicates 10.45 to 10.65 volts, you probably have a shorted cell. A shorted cell is caused by plates touching, sediment (“mud”)build-up or “treeing” between the plates.

Battery Testing – Load Test
If the battery’s State-of-Charge is at 75% or higher or has an ugood55 built-in hydrometer indication, then you can load test the battery by one of the following methods:

  1. Turn the headlights on high beam for five minutes.
  2. With a battery load tester, apply a load equal to one half of the CCA rating of the battery for 15 seconds.


Battery Testing – Bounce Back Test
If the battery has passed the load test. After the load is removed, wait ten minutes and measure the State-of-Charge. The battery is okay if it has retained 75% SOC.

If the battery bounces back to less than 75% State-of-Charge (1.225 specific gravity or 12.45 OCV), then recharge the battery and load test again. If the battery fails the load test a second time or bounces back to less than 75% State-of-Charge, then you should replace it because it lacks the necessary CCA power.

Battery Testing – Recharge
If the battery passes the load test, you should recharge it as soon as possible to restore it to peak performance and to prevent lead sulfation.


Extend the life of your battery by:

– securing the battery firmly to the cradle, not too tight or too loose. Vibration will damage plates and shorten battery life.

– keeping battery cables and terminal connector clean and tight, corrosion prevents electrical flow which can severely diminish charging current and reduce ability of battery to start the vehicle.

– checking your electrical charging system regularly and making sure it’s working properly. Over or undercharging will impact the positive and negative plates causing a dramatic reduction in the life of the battery.

– checking electrical wiring and load. Electrical leakage or short will drain your a boot light or accessories left on can drain your battery overnight.

– using the right battery for the application, battery should be the same or bigger than the OEM fitment, under size battery will fail early.

– using automotive battery for starting application and deep cycle battery for deep cycle application (TV, fridge, trolling etc), EFB & VRL range for Start-Stop vehicles.

– keeping sparks and flames away from battery, battery creates explosive gases when charging.

– keeping your battery fully charge when not used frequently. – keeping the electrolyte level above the plates (for accessible types only).