There is nothing wrong with DMM. Usually it display nearest and closest values of Voltage or current etc. I tell you the way to check cutoff point then update us with results:
First note that 3 points/dots are charged and display on led display fully and when 4rth point is charging or running then measure the values of voltage at different time until 4rth point will charged- this will give you idea what is actual cutoff voltage and when all points are fully strong/charged then it will tell you floating voltage which should round about 13.66V or some near values.
If your values are not up to spec then go to College road if you live in ISB/RWP, you will find many shops there who repair your inverter according to specs by using same components used by homage and their rates are also less then homage which ripping the people by putting cheap components on pcb and will cause many problem in futures.