Don't bother with a calcium, these discharge even quicker when not in use.
How much do you want to spend ?, your ideal battery is a AGM, ie absorbed glass mat, this will rape your wallet to the tune of around £110, but will have almost zero discharge compared to a std lead acid or calcium battery.
All batteries will self discharge, of any type, AGM discharge the leastm lead acid tend to lose 1% a day, calcium 1 1/2% - 2% a day, AGM(a good one) is 1% a week, ideally need to be above 80%.
AGM also don't get damaged if fully flattened, unlike all the others, and have massively superior cranking power, a 70ah AGM will be 1000 amps easily.
If fitting a calcium battery to a car with a std charging system such as yours it will never fully charge to it's potential, as voltage on calcium equipped cars is higher up to around 15.8V, will work ok at lower voltage of lead acid battery but you'd be paying extra for a benefit you can't get, and a disadvantage you don't want.
tabetha