Deep Cycle Battery
A class of battery built so that it can give up a large part of its capacity and be recharged over and over. Thick plates, durable separators and high-density active material are used. Hundreds of cycles are targeted in lead-acid types and thousands in LiFePO4.
Deep discharge capability is less about how much energy a battery stores than about how many times it can give that energy. In lead-acid chemistry every discharge-charge cycle leaves a small irreversible change on the plates; thick plates slow this wear down.
The numerical frame is as follows: a lead-acid or AGM deep cycle battery typically gives 500–1000 cycles when the depth of discharge is limited to 50%. If the same battery is discharged 80% every time, the cycle count roughly halves. In other words, choosing a large battery and discharging it little is usually a cheaper strategy than choosing a small one and discharging it deeply.
In an RV this choice feeds straight into comfort. Loads such as levelling, the water pump, the refrigerator and lighting take a certain percentage of the battery every day. If you do not calculate the capacity in terms of usable energy, a battery bank that seems adequate in the first season will give a noticeably shorter camping time within a few years.
Context in which this term is used: RV automatic levelling guide