Absolutely ... We have the MXS 5.0 ...five or six years old now and still going strong. Bought direct from CTEK but as above you could probably save a little by buying from Lazada. You might find the XS 0.8 too small as it meant for motorbike batteries, and it will take a long time, if at all, to charge a car battery.
AS mentioned above your battery should not drop any voltage in a week. If you have a decent multimeter you could check the parasitic draw. If you don't know how ...google.