I do not recommend you installing the battery yourself, if you don't know what you are doing. As simple as it may look like and sound, I have seen owners burning out their ECU or TCU, in the end will costs them even more money in repairs besides changing a new battery.

Rubbish.
This is not Genting or some cold winter country weather.
Even Genting goes right down to 20C still the car can start.

Whether you park at basement or I park in my car porch, ambient temperature doesn't affect vastly.
Its only if your car has parasitic battery drain, then it's an issue. Just like Roman Catholic also mentioned earlier.
Parasitic drain is when an accessory in your car drains excessively even when the ignition is off.

All you need is a clamp volt meter and some technique to check for that

Gawd, is this how Bateriku techs scam their way to non knowledgeable customers , in selling their batteries 

Yes, especially if it is a verified good new battery. Unless one has checked carefully everything, then only can one eliminate parasitic drain as a probable cause.

It is good never to tamper with electricals irregardless whatever the accessory shop guy has to say.

Oh it is a 3 year old battery, I was thinking about it but your writing sure didnt sound like it.

So far I have only come across 1 case of parasitic drain and it takes about a week to drain down the battery.

So yeah, without any battery test done for confirmation, I would guess that it is an old battery unable to hold its charge any longer.  There is no point trying to salvage it or worse still, it is a battery with a bad cell(s). Never charge any battery with bad cell(s).