First off a full model and serial number would help us greatly to be able to give you more accurate information.

with that said:

genie scissor lifts do not have a scantool, they are usually self diagnostic and display a message on the controller status window or LED indicator.
If you have slow lift which according to your voltage this may be the cause, 24.5v is low. A fully charged battery pack should ready 25 to 26v or even higher depending on how new and the condition of the cells in the batteries.
Check the cell voltages, they should be reading about 2.1 to 2.3v per cell. Also check your charger output to make sure it is working correctly. Check the date code on the batteries, if they are more than 3 to 4yrs old they may be failing.

Once you verify your batteries and are sure they are in good condition:
Check your voltage drop at the lift solenoid.
The voltage you say you have at the motor seems quite a bit low, it should be near battery volts under load.

And yes, genie does have service manuals on their website that are free to download (remember they do not cover every scenario but they are helpful for alot of things. ;o)

Genie has service manuals on their web site. You should find what you need there.