Battery Basics

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BATTERY CAPACITY RATINGS
Several battery capacity ratings have been established by the Battery Council International (BCl) that determine the current capacity of a battery. The current capacity is an indication of the battery's ability to develop and deliver high amperage current to the starter and provide reserve power to the electrical system.

1) COLD CRANKING AMPS
The first battery rating is the cold cranking amps (CCA) rating. This rating indicates the ability of a battery to deliver a specified current at low temperature. The rating is determined by the amount of current a fully charged battery can supply for 30 seconds at 0'F (- 17.8'C) without having the battery terminal voltage fall below 7.2 V.

2) CRANKING AMPS
The second battery rating is the cranking amps (CA) rating (not to be confused with COLD Cranking Amps), which is the battery's ability to deliver a cranking current at 32' F. This CA Rating is the same test as in the CCA rating, except it is calculated at a high temperature. A battery with a CA rating of 800 may confuse a technician who may assume it is a CCA rating number. To convert CA at 32 'F to CCA at 0 'F, divide CA by 1.25. Example: a 650 CCA rated battery has the same current capacity as a 812 CA rated battery. This apparent marketing ploy may confuse the public into thinking they are purchasing a battery which is higher in capacity than it really is.

3) RESERVE CAPACITY
The third battery rating, the reserve capacity rating, is the time in minutes a vehicle can be driven after the charging system fails. This is roughly equivalent to the conditions after the alternator fails while the vehicle is being driven at night with the headlights on. The battery alone must supply current to the headlights and the computer/ignition system. The assumed battery load is a constant discharge current of 25 A. The reserve capacity rating is the length of time a fully charged battery that is at a temperature of 80'F (26.7'C) can supply 25 A before the terminal voltage falls below 10.5 V.

4) AMPERE HOUR
The fourth battery rating, the ampere-hour rating (expressed in ampere-hours, or Ah) is the amount of current a fully charged battery can supply for 20 hours without having the terminal voltage fall below 10.5 V. This test is made at a temperature of 80'F (26.7'C). If a battery can deliver 4 A under these conditions, it is an 80-Ah battery (4 A X 20 hours = 80 Ah).