Renault Scenic check emissions

car would not start called out AA Enginner said that the battery had lost a cell need new battery! new battery fitted. on dashboard warning lights came on check emissions after a few days the car would not start again! back to the garage car tested to prove that the altenater is ok and charging the battery.renault enginners said that this battery had lost a cell after a diegnostic check. back to the garage for another new battery,then back to renault for another diegnostic check found after this second check eg;dephazer valve. this was not found on first visual health check .have now got a bill for £900+to fix the car on top of the cost of the battery that may not have been at fault in the first place.