Two things come to mind:
1) The battery was not fully charged.
2) The battery is junk.

You might be able to determine which is the case by checking the specific gravity of the cells. The SG of a new fully charged cell is 1.275. At 60% charge it drops to 1.20. All the cells should be within +/- 0.050 of each other.

With an old but still functional battery the full charge SG can be a little less and the variation between cells can be a little more. If one cell is 0.100 or more less than the others the battery is on its last legs.

You will have to peel off the plastic strip on the top of the battery to get to the individual cells. Battery acid is serious stuff. It can eat your clothes, burn your skin or blind you. Use an appropriate level of caution (wear safety glasses).

If the battery checks out you may have a serious drain somewhere. That involves a different diagnostic tree.

Greg