Problems With Using Too Large of an Auto Batteryby John Walker
Car manufacturers evaluate the amperage necessary for starting and operating the vehicle in different situations to determine the alternator needs. The whole charging system is based upon the evaluation of the vehicle's needs. The battery is just one aspect of the system. Using the wrong battery in a vehicle carries several potential issues.
The alternator installed in your vehicle is set to produce sufficient amperage to charge the battery while running the vehicle. A larger battery will initially have no impact on the alternator, but will pull greater amps during vehicle operation, causing the alternator to wear out sooner. Some people believe a larger battery is needed for after-market electronics. Change your alternator instead as electronics operate off the alternator, not the battery.
Most modern vehicles run all the systems through an on-board computer. The charging system is regulated by different controls. Installing a larger-capacity battery changes the currents, which could lead to spikes and surges that may damage the on-board computer or fuse panel. You have a lower chance of damaging the computer, but with alternator failure, damage is still a possibility. The fuse panel likely will receive most of the damage.
The fuse panel protects the electrical systems from spikes and surges. A larger battery creates a situation where electrical current can fluctuate. One of the first things that may be impacted is the regulator on the alternator -- which would allow the direct current to change to alternating current. Radios, amplifiers and other electronics could receive damage as a result. However, the chance of damage is minimal.