There is a Festool promo around at the moment, if you have one of their vouchers and buy a bare kit, i.e. cordless tool without battery they will supply a 5.2Ah battery for free.
Two slight issues, first you need to get your hands on a voucher and most of their bare kit doesn't include the charger so unless you are already using that platform, that's another cost.
I replaced my cordless kit last year and boiled it down to three main players; Fein, Panasonic and Festool. I ultimately went with Fein and now kinda wish I'd gone one of the other two. I'm fairly Festooled up to the eyeballs but could never justify the cost of their drills (other than the CXS which is a no brainer) however their prices seem to be coming down lately.
If I remember correctly, I think FFX are doing deals on Panasonic at the moment and they rate quite highly, particularly the batteries.