This paper presents the results of the development of VRLA(value regulated lead acid) battery over 1000 cycles at D.O.D(depth of discharge) 50% suitable for photovoltaic power generation system. This battery was made of gel electrolyte and tubular positive plates. Ths cycle-life was carried out for 1450 cycles at D.O.D 50% with 3H.R.(hour rate) and 1150 cycles at D.O.D. 100% with 5 H.R. As we expected, we could get cycle-life over 1300 at D.O.D 100% in lab test. However, the positive active mass of a tubular-type gelled lead acid cell was changed morphologically to a great extent during the deep discharge-charge cycles. In order to reduce these changes, the effect of filling denesity on the active mass has been also studied. When suitable filling denesity is applied to a positive plate, filling denesity of the positive active mass was suppressed ans the structural changes became smaller. The cycle-life of the postitive plate increased remarkably by suitable filling density due to suppression of the decrease in cohesion and improvement of the electrochemical reaction between PbO2 particles. the total water loss for gel battery was found to be depended on charging conditon, space, and filling density.