Rentech Batteries what a joke

I bought an Inverter and had the misfortune of getting it with a Rentech JPC12-100aH Lead Carbon Battery Rentech profess that the Battery will give 2200 Cycles at 50 % load. I bought the Unit 31 May this year. It's easy to work out that there hasn't been 2200 Cycles yet. The Battery has now deteriorated to the extent that it lasts 20mins. This happened 3 weeks ago already and the people where I bought the unit in Jefferies Bay informed me that they are getting no joy from Rentech. I believe that the sentiment from Rentech is " take us to court ". I got this unit for my daughter who is reliant on it for income as she does online classes. I really hope Rentech will stop the bully tactics and take us small guys into consideration when they flood the market with inferior poducts and great promises. I bet my last Dollar they will not respond to this.