Sooner or later, a load draw will snap the plate connection open and the battery fails. Overcharge seems like a simple problem to cure. If all you lost by undercharge were a few Amp-hours of capacity, then undercharge would be a solution. Undercharge destroys batteries in a different way, however, by a buildup of lead sulfate. Only a correct charge will obtain maximum life from batteries.
Many people are completely unaware of the loss of capacity from their batteries due to undercharge.
Even worn-out batteries will start an engine, the test used by many to gauge life left in their batteries. To fully charge a battery requires that its terminal voltage rises to about 14.4 Volts. If permanently applied, this voltage would boil all of the electrolyte from the battery and might even cause a condition called thermal runaway. With thermal runaway, the battery gets extremely hot and may even explode, spewing acid everywhere. While 14.4 Volts is required to fully charge batteries, a voltage under the gassing potential of 13.8 Volts is necessary to prevent overcharge.