@XplorerInstalling a bigger battery does not mean the charging system won't charge it. Most cars with 12V charging systems put out 14V. Cranking power does matter but vehicle options such as air conditioning and a number of major electrical accessories may indicate the need for optional heavy duty battery with higher ratings. Remember, to handle cranking power and the vehicle's other electrical needs, the replacement unit should never have lower ratings than the original battery.
@wasay_ahmed
My personal opinion... You don't need a bigger battery just for an audio system, unless you are going to have the audio system on while the car is turned off.
Anyway... Here is some stuff about batteries for your info... Writing from notes I took last year in college...
Battery Cables
Battery cables must be sufficient capacity to carry the current required to meet all demands. The normal 12-volt cable size is 13mm to 19 mm (4 or 6 gauge).
BATTERY VOLTAGE AND CAPICTY
Cell size, state of charge, rate of discharge, battery condition and design, and electrolyte temperature all strongly influence the voltage of a cell during discharge. When cranking an engine, the voltage of an average battery at 26.7C (80F) maybe about 11.5 to 12 V. At 17.7C (0F), the voltage is significantly lower.
At low temperatures, the viscosity of the electrolyte increases, making it more difficult for the acid to move freely into the plate pores and around the separators. This slows the rate of the chemical reaction and lowers battery voltage, limiting the output of the battery, especially at cranking rates.
Battery capacity is the ability to deliver given amount of current over a period of time. It depends on the number and size of the plates used in the cells and the amount of acid used in the electrolyte.
BATTERY RATING METHODS
Batteries are rated according to reserve capacity and cold-cranking power.
Reserve Capacity
A reserve capacity (RC) rating represents the approximate time in minutes it is possible to travel at night with battery ignition and minimum electrical load, but without a charging system in operation. The time in minutes is based on a current draw of 25 amps while maintaining a minimum battery terminal voltage of 10.5V (12-V) batteries at 26.7C 80F). A battery with a reserve capacity of 100 would be able to deliver 25a for 100 min. before the voltage would drop below 10.5 V. This rating represents the electrical load that must be supplied by the battery in the event of a charging system failure.
Ampere-Hour Rating
The ampere rating is the amount of steady current that a fully charged battery can supply for 20 h at 26.7C (80F) without the cell voltage falling below 1.7V or 10.5V at the terminals. For example, if a battery can be discharged for 20 h at a rate of 4.0A before its terminal voltage reads 10.5V, it would have a rating of 80 A/h.
Watt-Hour Rating
Some battery manufacturers rate their batteries in watt-hours. The watt-hour rating is determined at -17.7C (0F) because the battery’s capacity changes with temperature. The rating is determined by multiplying a battery's amp-hour rating by the battery's voltage.
Cold Cranking
A cold cranking amperes (CCA) rating specifies the minimum amperes available at -17.7C (0F). CCA is the common standard for low-maintained batteries. The rating allows cranking capability to be related to such significant variables as engine displacement, compression ratio, temperature, cranking time, condition of engine and electrical system, and the lowest practical voltage for cranking and ignition. The rating indicates the amperes that a fully charged battery will maintain for 30 seconds without the terminal voltage falling below 7.2 V for a 12-V battery. The cold-cranking rating is given in total amperage and is identified such as 300 CCA, 400 CCA, and so on. The usual range for passenger cars and light trucks is between 300 and 600 CCA; some batteries have a rating as high as 1100 CCA.
Cranking AMP Rating
This rating is similar to CCA and is a measure of the number of amperes a battery can deliver at 0 C (32F) for 30 seconds and maintain at least 1.2 V per cell (7.2 V in a 12-V battery). The rating is more commonly used in climates that rarely see close to -17.7C (0F) temperatures.
