Pss invertor and batteries

Bought a 5kvs invertor with 4 batteries which cost alot of money a year later the batteries are faulty and dont even last 30min , pss came with all excuses about power outages damaging the battery but that is what the invertor and batteries are for.the batteries are 1 year old and they say there batteries have a 10 years life span. They refuse to sort the issue out and told me I must purchase new batteries which is over R10k, how can u replace batteries every year for R10k??? Do not every use them they are useless and will find every excuse not to sorr out the problem they also charged me over R1000 to come out to look at the unit