Having covered 50 or so miles - motorway speeds

- pulled up for 15
mins got back on went to start up battery flat, got a jump start
went to pull away conked out, RAC came out charged battery for
10mins got me home, charged up over night and left for a week,
checked the battery still had full charge, started up didn't drop a volt
put lights on went down a volt, turned lights off went up a volt
but have not ridden due to me thinking that i prob need a new alternator my mate reckons as it was such a hot day aswell that it
this could have something to do with it?