Waspy buzz buzz hullo! AND ADVICE PLEASE!

Hello! Newbie here. Glasgow southsider.
Just got my first wee moped, it's a WK wasp 125.great wee runner. Never had much interest in bikes etc, just wanted a wee runaround.
Hoping you can also help me... I've just put a new battery in it, cos it seemed to be going flat a lot.
now that I've not used it in exactly one week, it's flat again.
Can anyone please suggest whether I should get a trickle charger, or maybe go have it checked out. If the latter, does it go to a normal garage, or bike specific mechanic? I don't know if this is normal, anyway . I'd probably understand if it'd been left over winter, but one week?

I really am clueless to this, so be nice!! Cheers

 

If it has an immobilizer on it this may be the problem draining battery
If you have a socket you can plug a trickle charger in be best so always battery charged up if left connected when not using