based on the service literature on this model/serial lift if the shutdown and charged lights are flashing it is indicating the batteries are 100% discharged.
The description of this fault is:
"Batt Is 100% Discharged: Based on 1.75Vdc / cell, this error is produced when cell voltage falls below this value (example: 21Vdc for 24V Battery Pack). A.C. Power should be connected to charger and charging initiated immediately."

Now in this case the charger will not start up at all until it sees the voltage it wants above the 21vdc. There is only one way to achieve this, get the voltage higher by either replacing the batteries or you can find a good charged battery pack and connect it in parallel and fake out the charger so it will start up in normal mode and start charging. I would leave it on for a few minutes till it brings up the lower set of batteries enough so the charger will be able to continue on it's own, THEN you remove the jumper pack so it can continue.
I would monitor the charging periodically as it may error out again with an over heat code if the charger is charging too hard.
Once you get the batteries charged up enough you can run a load test on each battery and see if any of them have any bad cells or if they all are just not capable of charging due to old age or something along those lines.