Deep cycle batteries are batteries that are made to have its capacity deeply discharged and recharged on a regular basis. During the discharging cycle a deep cycle battery’s electrolyte begins to harden onto the lead plates and become inert and unusable lead-sulfate for the time being. During the charging cycle the electrolyte that hardened onto the plate gets soft and once again becomes active material; ready for use by the battery. This is the normal operation cycle of the battery.
After many cycles the electrolyte will start to deteriorate and decay your lead plates (this can be seen as a black “cloud” in the clear acid) and harden onto the remaining surface of your plates forming a barrier between the lead plates and the remaining active electrolyte; causing the battery to cease function. This is called battery sulfation.
Solar batteries are made with considerably thicker lead plates to withstand multiple more years of normal operation and sulfation. As a result our batteries typically have a life span of 10-15 years although many of our customers are still using the batteries from 20-25 years ago with no issues. Solar batteries are made to be deeply discharged on a daily basis because the power your system will draw at night (when there’s no light) will come from the batteries. This is why solar batteries are some of the longest living deep cycle batteries on the market.