Battery Basics

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, a solution of sulphuric acid and water. In a typical lead-acid battery, the voltage is approximately 2 volts per cell, for a total of 12 volts. Electricity flows from the battery as soon as there is a circuit between the positive and negative terminals. This happens when any load that needs electricity, such as the radio, is connected to the battery.

Most people don’t realize that a lead-acid battery operates in a constant process of charge and discharge. When a battery is connected to a load that needs electricity, such as the starter in your car, current flows from the battery. The battery begins to be discharged.

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.

As a battery discharges, the lead plates become more chemically alike, the acid becomes weaker, and the voltage drops. Eventually the battery is so discharged that it can no longer deliver electricity at a useful voltage.

You can charge a discharged battery by feeding electrical current back into it. A full charge restores the chemical difference between the plates and leaves the battery ready to deliver its full power.

This unique process of discharge and charge in the lead-acid battery means that energy can be discharged and restored over and over again. This is what’s known as the cycling ability in a battery.

Why won’t my vehicle start?

If the battery won’t start your vehicle, you usually refer to it as “dead,” even though that’s not technically correct. A battery that’s merely discharged – from leaving your headlights on or from a damaged alternator – can be recharged to its full capacity. But a battery that’s at the end of its service life can’t be recharged enough to restore it to a useful power level. Then it truly is dead, and must be replaced.

If the battery is discharged and not dead, you can jump-start it from another fully charged battery. About 30 minutes of driving may allow the alternator to fully charge the battery. But if the alternator or another part of the electrical system in your vehicle is damaged, the battery will not recharge and a mechanic or service station also will not be able to recharge it. So if your battery keeps discharging, have your electrical system checked before you replace it. What looks like a bad battery could be an electrical system problem. If you have a bad component in the electrical system, it will keep draining a new battery, and you’ll be stranded again and again.

The Anatomy of a Battery




Battery Safety Handling

  • Always wear proper eye, face and hand protection when working with batteries
  • Never lean over a battery while boosting, testing or charging
  • Exercise caution when working with metallic tools or conductors to prevent short circuits and arcing
  • Keep terminals protected to prevent accidental shorting
  • Replace any battery that has signs of damage to the terminals, case or cover
  • Install battery in a ventilated area for operation and during charging

Download the SDS VRLA and SDS WET Lead Acid to get information on battery content, safety and handling, and emergency measures.


Cycle Capacity Comparison

No matter how you like to spend your free time, whether it’s on the high seas, the open road, or playing the fairways, we offer a perfect VARTA® Professional battery for you. Remember, it pays to choose a battery with a higher cyclic durability as they have a longer service life – it’s always good to do a cycle capacity comparison.


Battery Application and Installation

  • The battery is not being used in the application for which it was designed
  • The battery is not sized properly for the application
  • The vehicle has excessive electrical accessories
  • The battery is not properly fitted into the vehicle
  • The battery cables are not clean
  • The battery cables have not been properly adjusted to fit the battery terminals

Battery Service and Maintenance

  • The vehicle’s electrical system has been repaired or altered
  • The vehicle has been stationary for a long period of time
  • The vehicle has been brought in from or driven in another part of the country for a long period of time

Visual Inspection of Battery

  • Terminals show signs of having been hammered, twisted or driven down into the cover
  • Side terminals show signs of over-torquing
  • Container or cover show signs of stress, damage or high temperature.
  • Ends of the battery are pushed out indicating plate growth

Powersports AGM battery fitment & filling

We do not recommend that our VARTA® Powersports AGM batteries are tilted or laid on their side for either fitment or charging. These batteries are spill & leak-proof at angles of up to 45˚, as soon as they’ve been filled in accordance with the filling instructions (e.g. allowing 20 minutes acid absorption time).

Powersports AGM battery fitment & filling

  • Absorbent Glass Mat (AGM)
    • The mat of micro glass fibers which is used for filtering the sulfuric acid in lead batteries. The distinguishing feature of an AGM Battery.
  • Acid Stratification
    • When charging a lead acid cell, high density acid is produced in the plates. This heavy acid drops as a result of gravitation to the lower part of the cell while lower density acid rises to the top of the cell. This stratification of acid can cause loss of capacity and/or battery failure.
  • Active Material
    • The active material in the positive plates is lead dioxide and that in the negative is metallic sponge lead. When an electrical circuit is created, these materials react with sulfuric acid during charging and discharging according to the following chemical reaction: PbO2 + Pb + 2H2SO4 = 2PbSO4 + 2H2O
  • Ampere (Amp, A)
    • The unit of measure of the electron flow, or current, through a circuit.
  • Ampere (Amp) Hours
    • A unit of measure for a battery’s electrical storage capacity, obtained by multiplying the current in amperes by the time in hours of discharge. (Example: A battery which delivers 5 amperes for 20 hours delivers 5 amperes x 20 hours = 100 Amp-Hr of capacity.)
  • Battery Case
    • Battery box containing the plate blocks, the connectors and the electrolyte.
  • Battery Charger
    • Unit supplying electrical energy to a secondary battery. Product release: Battery Chargers.
  • Battery Test
    • This term describes the test for determining the charging condition and electrolyte level of lead batteries with liquid electrolyte. The charging condition is determined by measuring of the acid density.
  • Capacity
    • The ability of a fully charged battery to deliver a specified quantity of electricity (Amp-Hr, AH) at a given rate (Amp, A) over a definite period of time (Hr).
  • Cell
    • The basic electrochemical current-producing unit in a battery consisting of a set of positive plates, negative plates, electrolyte, separators and casing. There are six cells in a 12-volt lead acid battery.
  • Charge Acceptance
    • The quantity of current in ampere hours which a battery in a defined charge state can accept at a specified temperature and charge voltage within a defined period.
  • Circuit
    • The path followed by a flow of electrons. A closed circuit is a complete path. An open circuit has a broken or disconnected path.
  • Cold Cranking Rating
    • Number of amperes a lead acid battery at 0°F (-17.8°C) can deliver for 30 seconds and maintain at least 1.2 volts per cell. Very important for the operation of snowmobile batteries.
  • Container
    • The polypropylene or hard rubber case which holds the battery plates, straps and electrolyte.
  • Corrosion
    • The destructive chemical reaction of a liquid electrolyte with a reactive material – e.g., dilute sulfuric acid on iron, producing corrosion products such as rust.
  • Cover
    • The lid for the container.
  • Current
    • The rate of flow of electricity, or the movement of electrons along a conductor. The unit of measure for current is the ampere.
  • Cycle
    • In a battery, one discharge plus one recharge equals one cycle.
  • Deep Discharge
    • State in which a cell is fully discharged using low current, so that the voltage falls below the final discharging voltage.
  • Discharge
    • When a battery is delivering current, it is said to be discharging.
  • Electrolyte
    • In a lead-acid battery, the electrolyte is sulfuric acid diluted with water. It is a conductor that supplies water and sulfate for the electrochemical reaction: PbO2 + Pb + 2H2SO4 = 2PbSO4 + 2H20
  • Fading
    • Long-term loss of capacity during use.
  • Failure
    • A state in which a battery no longer functions satisfactorily. There are several forms of failure.
  • Failure, permanent
    • A state in which a cell or battery cannot be recharged to a satisfactory level.
  • Failure, reversible
    • A failure condition that can be remedied by using particular electrical procedures or by reconditioning.
  • Final charging current
    • The final charging current is the current at the end of an IU charging operation (gassing current).
  • Final discharging voltage
    • Indicates the lowest allowable voltage level that a battery or cell can be discharged to. Discharging to below this cutoff voltage (deep discharge) can impair or (through pole reversal) destroy the electrochemical cell in the case of various battery types (e.g. lead, Ni/Cd, NiMH).
  • Forming
    • Initial electrical charging for converting the active masses into the charged state .
  • Frame
    • The reinforced outer parts of a battery grid.
  • Grid
    • The lead alloy framework that supports the active material of a battery plate and conducts current.
  • Ground
    • The reference potential of a circuit. In automobile use, the result of attaching the battery cable to the body or frame of a vehicle which is used as a path for completing a circuit in lieu of a direct wire from a component. Today, over 99% of automotive and LTV applications use the negative terminal of the battery as the ground.
  • High Current Charging
    • Charging with a current strength greater than 1C.
  • High Current Discharging
    • Discharging with a current strength greater than 5C.
  • Impedance
    • Apparent resistance of an alternating circuit to current; composed of reactance and ohmic resistance.
  • Industrial Battery
    • A storage battery which is used to supply power to industrial equipment (e.g. fork-lift trucks).
  • Initial Charge
    • The initial charge is the first charging process after the electrolyte has been poured into a dry precharged battery. It has the purpose of bringing the cell or battery to full initial capacity.
  • Initial Tempertature
    • The temperature of the electrolyte in an accumulator when discharging or charging begins.
  • Initial Voltage
    • A battery’s initial voltage is the working voltage when discharging begins. Measurement usually follows, as soon as current has flowed long enough for the voltage to remain at a constant level, for example, after 10% usage of a previously fully charged cell.
  • Inner Resistance
    • Ohmic resistance of a battery.
  • Inner Ressistance, Effective
    • The measurable resistance against the flow of current in a battery expressed as a drop in the battery voltage proportional to the discharging current. The value is dependent on the manner of construction, the charge state, temperature and the age of the battery.
  • Insulation Resistance
    • The resistance between a cell or battery and a mass/earth (motor-vehicle body, torso).
  • JIS Code
    • Powersports batteries are tested according to the JIS Norm Standards ; in that case JIS D 5302. : 2004 Edition. This Japanese Industrial Standard norm is relevant for SLI Lead-acid batteries for motorcycles. This standard is stipulating the types, structures and tests of lead-acid batteries included in the last revision for the VRLA ( valve regulated lead-acid ) also the tests methods.
  • Lamp Black
    • A fine carbon powder used as an ingredient for negative lead masses. Component share ≤ 0.5%.
  • Lead (Pb)
    • A chemical element which belongs to the heavy metals (specific weight 11.341 g/cm³). It is used in the form of bivalent and / or quadrivalent compounds (PbSO4 or PbO2), as porous sponge lead for active masses and as lead-antimony or lead-calcium alloys for grids in lead batteries.
  • Lead Battery
    • An accumulator in which the electrodes consist primarily of lead, whereas the electrolyte consists of diluted sulfuric acid. Product release: Automotive Batteries Catalog.
  • Lead Dioxide
    • Quadrivalent lead oxide (PbO2), which is generated electrochemically during formation and which forms the active mass of the positive lead electrode. Color: black-brown.
  • Lead Oxide (Litharge)
    • A bivalent lead oxide (PbO), which can occur in two modifications: the orthorhombic, yellow high-temperature modification and the tetragonal, red modification. It is used in producing active lead masses.
  • Lead Sulfate (PbSO4)
    • Chemical compound produced on the positive and negative plates of a lead battery during discharge. It is the result of a chemical reaction between the sulfuric acid and lead dioxide of the positive electrode or the metallic lead of the negative electrode.
  • Lead Sulfate, Tetrabase
    • Chemical formula 3 PbO
  • Lead, Free (Pbmetallic)
    • Non-oxidized residual lead in cured lead plates. See Curing.
  • Lead-Calcium Alloy
    • A lead alloy for grids used in maintenance-free lead batteries. The typical calcium component is approx. 0.08%.
  • Lead-Coated Part
    • A metal part with a thin protective coat of metallic lead that has been deposited on the surface by galvanization.
  • Lignin
    • General term for the non-cellulose wood component (lignin sulfuric acid or desulfonate sulfuric acid). It is the main component of the additives for negative lead masses with a component share of ≤1%. It is sold under the name Vanisperse.
  • Load
    • Describes the current in amperes with which a fully charged battery can be loaded over a defined period and at a defined temperature without the voltage falling below a prespecified cutoff voltage.
  • Low Current Charging
    • Charging with a current strength that is only slightly higher than what is needed to compensate for self-discharge losses.
  • Low Current Discharging
    • Discharging with current flow under 0.1 C.
  • Machine Casting
    • A full or semi-automatic casting process for grids or small parts.
  • Maintained Capacity
    • The battery is kept in a fully charged state by means of a constant voltage charger with a low charging voltage (compensates for self-discharging).
  • Maintenance-Free Battery with Fixed Electrolyte
    • Lead-acid battery in which the electrolyte is held in place in a gel or microglass mat (AGM). The battery is sealed and is equipped with valves. It is highly stable and exhibits good cycling characteristics.
  • Mass, Active
    • The material in the electrodes that takes part in the charging and discharging reactions. In the nickel-cadmium cell, nickel hydroxide and cadmium hydroxide are used as active mass at the positive and negative electrodes. In the lead cell, lead dioxide and sponge lead serve as the active mass at the positive and negative electrodes. The sulfuric acid in the lead cell which functions as an electrolyte can also be considered as an active mass, because it also takes part in the cell reaction.
  • Mold, Casting
    • A component made of cast iron or steel in which the required geometry of the mold takes the form of a cavity (e.g. casting mold for producing lead grids).
  • Negative Electrode
    • See Electrode, negative.
  • Negative Terminal
    • Negative pole of a battery.
  • Nominal Voltage
    • See Voltage, Nom.
  • Ohm
    • A unit for measuring electrical resistance or impedance within an electrical circuit.
  • Parallel Connection
    • Connecting all the positive or all the negative poles of several batteries. This increases the capacity of a battery network while maintaining a constant voltage.
  • Paste
    • Mixtures of various compounds, (e.g. lead oxide and water, sulfuric acid) that are used to coat positive and negative lead battery grids. A distinction is made between positive and negative pastes depending on the recipe. These pastes are then transformed into positive and negative cured masses.
  • Plate- Negative
    • Cast metallic frame which contains a spongy lead active material. Reserve Capacity Rating (RC) – Number of minutes that a new, fully charged will deliver 25 amperes at 26.7°C/80°F and maintain a terminal voltage equal to, or higher than, 1.75 volts per cell. This rating represents the time the battery will continue to operate essential accessories if the alternator or generator of a vehicle fails.
  • Plate- Positive
    • Cast metallic frame which contains the lead dioxide active material.
  • Plug
    • Component with venting ducts for sealing a cell opening.
  • Polarity
    • Electrical term for describing the charge or voltage relationship between two electrodes.
  • Purified Water
    • Distilled or demineralized water for compensating the water losses in batteries requiring maintenance.
  • Rated Capacity
    • The capacity in Ah (as defined by the manufacturer) under defined discharging conditions (current, temperature).
  • Reaction, Reversible
    • Chemical reaction that can take place in either direction (oxidation or reduction). The cell reaction must be reversible in order to use a secondary battery (e.g. charging or discharging a secondary battery).
  • Recharging
    • Creating a fully charged state from any charged state (e.g. caused by self-discharging).
  • Reconditioning
    • Discharging with low current (e.g. I100) and recharging with approx. 30% overcharge. The procedure can be repeated if required.
  • Remaining Capactiy
    • The capacity that remains after discharging.
  • Remaining Charge
    • Full charge from undefined charge state.
  • Reserve Capacity Rating (RC)
    • Number of minutes that a new, fully charged battery will deliver 25 amperes at 26.7° C/80° F and maintain a terminal voltage equal to, or higher than, 1.75 volts per cell. This rating represents the time the battery will continue to operate essential accessories if the alternator or generator of a vehicle fails.
  • Self-Discharging
    • Self-discharging is a temperature-dependent permanent chemical reaction process at a cell’s or battery’s electrodes, without connection to a consumer.
  • Separator
    • A divider between the positive and negative plates of an element which allows the flow of current to pass through it.
  • Series Connection
    • Connection of the positive terminal of a cell / battery to the negative terminal of the next cell / battery. This increases the voltage of the battery network while keeping the capacity constant.
  • Service Life
    • The length of satisfactory performance measured in years or charging / discharging cycles.
  • Service Life, Cyclical
    • The number of cycles a battery lasts before its capacity falls below the acceptable value.
  • Service Life, Useful
    • The useful service life of an accumulator expressed as the period of time prior to its capacity falling to a specified component of the rated value.
  • Shock-Resistant
    • Battery protection against vibration achieved through design measures (e.g. fixing a plate block in position using hot-melt adhesive).
  • Short Circuit
    • An unintended current-bypass in an electric device or wiring, generally very low in resistance and thus causing a large current to flow. In a battery, a cell short circuit may be permanent enough to discharge the cell and render the battery useless.
  • SLI
    • Stands for Starting, Lighting and Ignition
  • Standard Charging
    • Charging current that can be maintained indefinitely without the need for special cells or switchable battery chargers. Under normal circumstances, cells can be charged overnight in 12 to 14 hours.
  • State of Charge (SOC)/Health (SOH)
    • The amount of electrical energy stored in a battery at a given time expressed as a percentage of the energy when fully charged.
  • Temperature, Nominal (Tnom)
    • An electrolyte’s nominal temperature is a specified value which is used as a reference value for capacity tests (e.g. according to European standard EN 60095-1, Tnom lies in the region of 25±2 °C for the 20-hour capacity of lead batteries).
  • Terminals
    • Electrical connection from the battery to the external circuit. Each terminal is connected to either the first (positive) or last strap (negative) in the series connection of cells in a battery.
  • Thermal Runaway
    • Continuous heating of the electrolyte up to the boiling point due to an increase in charging current as the charging voltage decreases (lead accumulator with falling charge characteristic).
  • Total Cost of Ownership (TCO)
    • Definition TOTAL COST OF OWNERSHIP Accounting technique •Shows all aspects/costs during life time of a vehicle: •acquisition •energy (fuel consumption) •repair and maintenance (tyres, batteries) •Shows main and hidden costs •Similar to Life Cycle Cost (LCC) For investment goods like buildings or production machines
  • Valve
    • A device allowing gas to escape when inner pressure is too high, while preventing air from entering.
  • Valve Regulated Lead Acid (VRLA) Battery
    • Batteries which are sealed and maintenance-free.
  • Venting Valve, Recloseable
    • Safety valve in the cell which opens in case of overpressure and closes again automatically when normal pressure has been restored (e.g. gel battery, AGM battery).
  • Volt
    • Unit of measurement for electrical voltage. Abbreviation V. Named after the Italian physicist and doctor Count Alessandro Volta (1745 – 1827).
  • Voltage and Temperature Dependent Cutoff (VTCO)
    • See Cutoff, voltage and temperature dependent.
  • Voltage Dip
    • A momentary drop in voltage when high current discharging is used (e.g. in the case of lead accumulators).
  • Voltage Drop
    • Should current flow through a resistor inside a closed electric circuit, a voltage drop will occur.
  • Voltage, Nominal
    • The battery’s average voltage during discharging with a low current strength. The manufacturer specifies the value on the accumulator (e.g. Ni/Cd = 1.2 V per cell).
  • Voltage Plateau
    • A slow decrease in voltage over a long period of time. Characteristic for many discharges of closed cadmium cells and closed lead cells. As a rule, the plateau extends from the first voltage drop at the start of the discharge to the bend of the curve after which the voltage drops rapidly at the end.
  • Watt
    • The unit of measure for electrical power, i.e., the rate of doing work, in moving electrons by, or against, an electrical potential. Formula: Watts = Amperes x Volt.
  • Welding
    • Connecting together two or more plates to form a plate block by welding on a connecting strap. See COS.
  • Working Capacity (Energy)
    • The working capacity of a cell or battery is the dischargeable electrical energy in watt hours [Wh] for an accumulator with average discharge voltage and corrected to Tnom.
  • Working Voltage
    • The working voltage of a cell or battery begins at its electrical connections as soon as an electrical consumer is connected to it; it is smaller than the nominal voltage.


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