Battery technology has come a long way in the last 10 years. Battery line trimmers are now comparable in power to petrol machines, but with little to no maintenance required. My suggestion would be to have a look at the range of 18-volt line trimmers, with my preference being towards the Ryobi range as they have fantastic versatility with their batteries. The same battery can be used in their entire range of 18V equipment. A great lightweight option would be the Ryobi-one 18V 305mm Cut Cordless Line Trimmer.