He is clearly not in the US ;-)
Yes the linked case has bit of parasitic drain. If it's in the last A1 version, it is not so bad. You can prove it is A1 by the button turns on/off USB port. The older version was not so good. See my thread about it.
About battery cells I can advise any brand name like Panasonic, Samsung, Sanyo, Sony, LG, .... For your purpose in this case Samsung 2600 are best price performance choice. Currently very good priced at Gearbest.
All in all you would spend just about 40 USD.