My car battery gets dead if I don't use the car for 10 days or more. Is it possible to charge it using 12v 2A power supply of my dth set top box. ?
EDIT: Just measured the voltages using DMM. Car battery=12.06 V and DTH Set Top Box suppy=12.43 V.
You could do this, but you'll have an issue. The charger isn't intelligent enough to know when to stop charging. This means over time it will over charge the battery, causing it to kill the battery in the process. A typical battery charger (at least newer ones) have systems built in which will charge the battery to capacity, then check it often enough to know when it needs a little something more, but won't overcharge and damage the battery in the first place.
There are plenty of "battery tender" type charges on the market which are a much better alternative. These are relatively cheap (under $20 here in the States), and provide the battery conditioning needed to keep your battery in tip-top shape without issues. Invest a small amount of money into this and you shouldn't have to worry about a battery except when the battery is worn out.
On that note, if your battery is at or near the five year mark, consider replacing it. You may also want to check your vehicle to see if there's a constant power drain causing your battery to go bad. You should be able to leave your vehicle for much longer than 10 days and still have the battery work without issue. There may be something else going on with the vehicle which you'll need to look into if it isn't.