1hr...3hrs.... like was already said, it takes good batteries at least 6 to 8hrs to charge if they are fully discharged. If you start opportunity charging them they will develop a memory and the runtime will be greatly shortened. This will also effect the charge time and it will become shorter as well. Once the batteries get in this condition they basically are useless for any practical use in shift runtime. You will wind up getting stranded without a lift while it charges and your operator is standing around twiddling his thumbs waiting on it.

save youself some trouble and bite the bullet and get some batteries. yes it is a heavy expense but in the long run you will see it was the wiser choice.