Battery Basics
The battery is the heart of a vehicle’s electrical system. So it is very important that a battery is capable of delivering the necessary electricity when called for and capable of accepting electricity when it is in a low state of charge.
Another important feature of the battery is that it acts as a giant capacitor in a vehicle’s electrical system. It absorbs many abnormal and transient voltages that are created by the various electrical components of the system.
If a battery is not up to specifications it will not deliver the necessary electricity, it will not accept electricity and it will not act as a capacitor. Consequently, the vehicle’s entire electrical system will be affected when this happens.
Battery replacement may be necessary if you experience any of the following: loss of power in cold or extended starts, slow or interrupted turnover of the starting motor, or if a battery discharge light on the vehicle instrument panel is lit (if equipped). If you are experiencing any of these symptoms, you should have your battery and/or electrical system checked.
Batteries are identified by test standards and rating methods that measure their ability and whether they have enough energy in reserve. These guidelines are set forth by the Society of Automotive Engineers (SAE) and the Battery Council International (BCI), a trade association representing the lead-acid battery industry.
GROUP SIZE
The BCI assigns a Group Size number to every battery. Vehicle manufacturers engineer batteries to meet their vehicles’ needs, then BCI assigns a Group Size number to that battery. This number identifies the maximum overall dimensions, terminal location and other features that affect the way the battery fits in the vehicle’s battery tray. For example, a Group Size 34 has the following dimensions: 10 1/4" length, 6 13/16" width and 7 7/8" height.
COLD CRANKING AMPERAGE
Cold Cranking Amperage (CCA) performance is a rating used to describe high-rate discharge capacity at low temperature. It is the discharge load (in amperes) that a new, fully-charged battery at 0 °F (-18 °C) can continuously deliver for 30 seconds and maintain a terminal voltage equal to or higher than 1.2 volts per cell.
Be aware that vehicles with larger engines and/or with more electrical accessories generally require batteries with higher CCA ratings. Make sure your replacement battery meets the minimum CCA performance. For example, a Group Size 34 Mopar 84 Series has 800 CCA at 0 °F (-18 °C), whereas a Mopar 72 Series for the same Group Size has 600 CCA.
CRANKING AMPS
This test/rating is performed at a warmer temperature than CCA ratings. Cranking Amps (CA), sometimes referred to as Marine Cranking Amps (MCA), is the discharge load at 32 °F (0 °C) that a new fully-charged battery can deliver for 30 seconds and maintain a minimum terminal voltage of 1.2 volts per cell.
RESERVE CAPACITY
Reserve Capacity (RC) is a rating that estimates the time a battery may last in the event of a charging system failure. RC is the time (minutes) which a new, fully-charged battery at 80 °F (27 °C) can be continuously discharged at 25 amperes and maintain a terminal voltage equal to or higher than 1.75 volts per cell, or 10.5 volts total for a 12-volt battery.
AMPERE-HOURS
Ampere-Hours (AH) ratings specify the current (amperes) that a fully-charged battery can produce steadily for twenty hours, maintaining a minimum of 10.5 volts. AH is seldom printed on automotive battery identification labels.
STARTING VS. DEEP CYCLE BATTERIES
Most automotive applications call for “starting” batteries that deliver high currents for short periods of time, such as when “starting” an engine. “Deep cycle” batteries often used in RV and marine applications are designed to deliver power for longer cycle times. Some batteries are dual purpose, i.e. starting and deep cycle.
A WORD ON SPECS
Vehicle electrical systems require batteries that provide certain power demands, in addition to the obvious size and terminal location requirements. Be sure to select a replacement battery that has the correct BCI Group Size number. Also make certain the vehicle’s minimum CCA and RC ratings are met. These specifications can be found on the O.E. battery label or an O.E. service manual.
Mopar Battery Reference List - PDF
