Alternator to recharge battery how far in Distance?

[DaveDreads]

My car sat on the drive for about a month and now i've got battery problems,
i've given it a bit of a charge and it starts.

I'm thinking of taking it for a drive down the motorway in the hopes that the alternator charges it up a bit,
I live in Coventry and I thought a blast down the M69 to Leicester would be a good run, it would be a round trip of about 60 miles,
how far in miles will I have to drive to get some decent charge in to it?

 

[H182]

If the battery is good shouldn't need that much if its going to be used daily. When mine was flat a 14mile trip to work was enough to charge it. Started fine going home.

 

[DaveDreads]

I put some charge in to it on Friday and it fired up no probs, but sat still Saturday & Sunday,
then this morning it was just dead, i'm charging it right now but haven't tried it yet, I just don't know how effective the
alternator is in relation to a charger.