Virago 535 1993 battery problem?

[Loreless]

I'm trying to get advice on a reoccurring problem

I'm riding a virago 535 1993, starts and runs nicely normaly but after driving for a wile if I stop it will sometimes not start. It attempts to turn over but fails as if the battery were flat (or close to). But if left for some, overnight etc. It will again start normaly.

I'm not sure wether its an alternator/charging fault or the battery not working properly after vibration during driving since it works of after it settles.

I've had this happen three times now in the last couple of months, in both cases where I've stopped then after a minute or so tried to start the engine, once after a medium 10 miles or so 40-70mph run, another after 30+ mile motorway run and the last time after just 10 minutes at 40mph.
I had to get jump started on the first and last but on the second I parked up and left the bike for perhaps 2 hours and came back and it started first time.

I've checked the fluid levels in the battery (a yuasa YB12A-A) and they are all in spec.

Do I need a new battery or should I be looking at the charging system? if anyones had and fixed this problem I'd love to hear from you, or any good advice.