Poor performance of OMNIPOWER batteries AGM GEL

I have purchased several AGM gel batteries from Sinetech based on the specifications for their omnipower range, in total 6 X OPR 120 AH, each time inside 12 months, the batteries have less than 20% capacity. on my 3rd warranty claim, supplying extensive data on my inverter configuration,(to spec) , to their recommended specification, they eventually agreed to warranty replace with 2 x OPR 240AH 12V. once again performance quickly starts deteriorating within lass than 100 cycles. 2 bouts of load shedding and these batteries have failed, less than 1 hour at 10A load and im at 70% DOD, when installed new with 20A load they reached 60% DOD in 6 Hours. 2 inverter upgrades and they claim inverters are damaging their batteries, I even supplied data showing a full discharge and bulk charge cycle showing all voltages and charging currents through the 3 stage AGM charging profile by both inverters, at no point was the profile out of spec. to summerise i have received better performance from AGM batteries at half the price point. they charge a premium for batteries claiming high life cycles yet perform dismally. I would think twice in investing in a product that from experience and cost do not perform as claimed, I will certainly move to lithium but will not invest in their range.