Sounds very gunged up, get it nice and hot and do a oil + filter change, with decent oil, clean out all pcv/breather pipes.
Certainly wouldn't hurt to strip and clean carb, leave all bits in thinners overnight if you can as this will disolve the gum and varnish.
As for battery, you could go fo a AGM, but will be £100 + easy, but beware, if it lists a CALCIUM battery as std fitment a calcium must go back in, otherwise charging system will cook a std lead/acid battery.
tabetha