Different angle on this one Tone. Have had this problem of low battery/clicking when trying to turn/start other cars/vans in the past.
It was usually one of the terminals on the battery not tight enough (or because they were a bit loose, oxidation of terminal built up and then gave bad conductivity). Usually a quick clean up of both terminal posts on the battery, good solid tightening of terninals then sorted the 'clicking' (arching) and got the thing going.
Worth a go after you've given that batter a good charge too hopefully
