How do accumulators age?

Let's say I have a Energy storage system that says it will last 1000 load cycles. I want to use it as a buffer for a Photovoltaik system. When it does no full load cycles but only 10% of one and then changes the direction of current does this decay the accumulator by 10% of a full load cycle and could therefore do this about 10000 times? How about not using it at all for a few days? It's a lead/acid cell if that makes a difference.