Help with Battery Terminal corrosion and why

Adding on to what Donn offered, acid corrosion is almost always related to outgassing while charging due to micro-fissures around the cell caps and battery posts caused by vibration over time or, in the usual case with a Jeep, due to excessive vibrations due to off road use. You can reduce it by rubbing some grease on the post, and around the post, but in the long run rough use, or time, will eventually result in microfissures leading to an accumulation of corrosion. This is why older batteries corrode more than newer batteries. To me the presence of excessive corrosion is a tell-tale sign the battery is nearing end-of-life.