i know it's been a week or so since you posted this so i'm just replying to see if you figured it out yet.
Going on you saying the machine may only be a year or two old based on what i find in the E30 service literature on bigliftsupport website this unit most likely has the curtis control system in it?
Has a BDI indicator along with an LED lamp?
I'd be curious to what the BDI level is showing, fully charged, discharged (yellow or red blinking led's on the scale)?. Is it showing any error codes before or during operation?

As for checking the batteries in general if they are fully charged you should be getting higher than 24v (12v on single battery).
You should be reading about 13.5 on a fully charged battery (25v to 27v on both together).
I would put the unit on the charger and test to make sure it is even charging, make sure the charger cycles through it's test when first turned on(if it has an analog needle indicator then it should show amp rate level), then with a multimeter hooked to the battery watch the voltage when the charger actually kicks into charge mode and see if the voltage increases, you should see a significant increase during charging with it gradually increasing. The charge voltage may even exceed the fully charged volts during the finishing charge time but as the battery cools down when the charger shuts off the voltage will level off and should settle at what the actual voltage is after charging. (around 25.5 to 27v).

Another thing to do is after charging run a volt drop test on the batteries, use the multimeter and hook across the batteries, note the voltage. Then operate the hydraulics, let it raise the forks to full height and stall the hydraulic pump, hold it there for about 15 secs and see what the voltage drops to. With a good condition battery it should not drop more than 1 to 1.5v, if you get a drop more than that you most likely have a spent battery or defective cell(s).

Then there is always the controller settings, using a curtis handset or pc service tool checking and making sure the factory settings are set correctly so that the highspeed is not inhibited by an incorrect setting. The service book has all the factory settings listed and can be easily checked.

But after all this being said i would lean towards it being a battery charge issue from your description.