Surrette Batteries S-600 6V, 450Ah (20Hr) Flood L-AcidWrite a review

I am a solar engineer in 2006 I installed an off grid system in the UK I used a 4000watt solar awray,an 8KW inverter and a 48 volt battery bank made up of 8x6-CS-25PS CV 820Ah in the year that the system has been running the the Rolls 5000 battery bank has had two faulty sells replaced.and over a 18hour discharge cycle they have never supplyed more than 450Ah there capacity 820Ah????