hello judy,
if the charger is indicating the charge is complete and shows 100% but the guage does not have the last green led lit then the batteries are not coming up to 100%. If they are old it may just be they are saturated/sulfated and are not actually getting to 100%.
On the guage face the ring around the outside consists of a fault light and 4 bdi led's. From the sounds of it only 3 of them are lighting up which confirms the battery issue. They should probably be checked, filled if they are not maintenance free. If any of them after charging still register below 2.1v per cell then you have a bad cell(s) not allowing it to come up to the 100% mark.
Now back to the LED's, The one on the bottom is the fault light, it should have a circle with a slash through it beside that led. When the alarm lights up and/or possibly if the battery gets in a very discharged condition it may also light up. Plus on the top side of the LED screen it will display the AL code and a small pictograph of a wrench will show as well.
Now in that same LED screen under normal conditions it should display the hours and show a small hourglass above it. If you saw that hourglass above that 5051 then yes, that would be the hours.
There is also one other pictograph of a turtle but that only shows up if you select slow mode.
If the unit is still not operating after charging and it will not activate and run when the handle is in the up position i still would suggest having that brake switch checked on the base of the handle/tiller arm.
The best way to diagnose the issue is by using a zapi handset diagnostic tool, it is more extensive in diagnosting fault (alarm) codes and can also run tests. Most technicians have those or a PC program they can plug in and run to diagnose the alarms and faults. The zapi controlled machines unfortunately rely on this method now and there are not many other options if all the external analog checks of other components fail to reveal a problem.

So first thing is check the battery and/or it's cells, a specific gravity test and the fluid level above the cell plates inside (unless it is a maintenance free sealed battery), a load test needs to be done to check for voltage drop to verify integrity of the cells staying power.
Does this unit have a large single battery or does it have a battery pack with 4 6v batteries in it? If it is a large (industrial type) then the load test will have to be done by a battery company. If it has the 4 smaller batteries in it they can be tested with a handheld battery load tester.
The reason i am stressing about testing and verifying the batteries is because if you have some bad cells, they may register a surface voltage that tells the BDI to show what it does but when the machine is turned on and a load is put on them they may drop below the voltage it takes to run the controller or turn on the system which may be triggering that code because it's not enough to make the brake switch work properly. But still the brake switch needs to be tested as well.
I'm sorry if this is long and drawn out but i have no quick answers to fix this quickly to just sell it. If the batteries are good and the brake switch is ok then there is more in depth troubleshooting needed.
At this point you have 2 choices, sell it as is and let the buyer deal with it, or hire a tech to come out and look at it and give you a precise answer to what is actually happening and what it will take to repair it.

Turned it on this am. Put it on charger over night. Charger says it's fully charged. Power comes on when I turn the key. The round display says 5051 (I believe this is the hours?). Three of the lights around light up on the outside of the circle. The very bottom and very top do not light up. But power is on. Still no movement an any direction or or up/down.

Is there a stop button that has been activated. The only other thing change is that this is not the original key. I noticed that a variety of keys can start this guy and my guys lost the original one.

Appreciate any help. Shutting down my business and I have a buyer coming for it today.

Hello Judy,
if what you saw on the display was AL 05 then this deals with the brake circuit.
The dash would display AL5, the controller would flash on it's LED 5 flashes, or the handset would indicate what the alarm is.
The condition is: Electric Brake does not release or remains released at all times.
The truck response: Traction and hydraulic functions disabled.
Possible causes:
-Damaged or loose electrical connection to brake. Verify electrical connection between electric brake and controller.
-Check brake coil for correct coil resistance. Disconnect brake. Measure brake coil resistance in both directions. Coil resistance should be 14.3ohms.
-Damaged fly-back diode at brake. Check coil resistance. Short circuit measured at brake connector may indicate a damaged diode. Cut(disconnect) one lead of diode and check with meter. If damaged, replace diode.
-Damaged controller. Activate the brake switch. Use voltmeter to measure voltage on wire 2C and 17 with brake connected in circuit. If both measurements are 24v and the alarm is displayed, then controller is damaged.

Note: the brake coil harness connects to terminals B-16 and B-5 on the controller plug. Wires in the harness are wires 2C and 17 which are Blue and Brown, wire 2C is brown, wire 17 is blue.
Also check the brake switch and make sure it is operating properly. (i would confirm this first). There are other things to check the tblshooting does not mention but we won't go there just yet. :o)