lifttrainer,

not sure what your meaning of an OPR is but i'm assuming you mean a sitdown rider electric that uses a larger industrial battery.

Using the comparison between a pallet jack and a larger rider truck and the chargers is not really a good comparison. Most likely they charge differently due to the type and size of the battery in the machine. Not to mention they cannot be plugged into each others chargers because of the battery connectors.
Pallet jacks use an SB175 size connector usually and the full size truck uses an SB350, No way they can plug into each others chargers.

I'm sure his low voltage problem is due to some other problem like edward hit on or maybe he has some issue with a motor short drawing too much power or something along those lines. Most of the time when batteries fall short of designed runtime it is usually a battery problem though, like a bad cable or connection or bad cell(s). And i have seen where the BDI settings were not set up correctly in the controller and causing the truck to run down too quickly.

Of course your point about the charger specs might be wrong could play a part in the way the battery charges up, that was a good point to consider :o)

How many other forklifts do you have that are the same battery voltage? The reason for asking is this, if you have three trucks that are 24vdc and two are OPR's and one is a pallet truck, for example, then the charger for the pallet truck charges at a different rate and amperage than the chargers for the OPR's. Here is another example, a pallet truck consumes 750 amps over a 6 hour period and an OPR consumes 1080 amps over a 6 hours period. If the OPR battery is plugged into the pallet truck charger, the OPR battery is basically being "short" charged. Look at the truck data plate and the charger data plate and ensure that they are both close the same value as far as the amp/hour rate is concerned. I hope this helps!

(best "ancient aliens TV series voice) Perhaps it MAY be that what ever is causing the lifting, is causing a load on the battery as soon as it is plugged in, and this giving a bad voltage reading to the BDI circuit. also perhaps a defective connection or spring in the battery connectors causing a voltage loss.
is it possible to swap out this battery into another unit for testing? or plug a different (same nominal operational voltage) truck into this battery? can you take voltage readings right at the battery cable connections? ?

If it shows 0 percent after a charge, then the battery is not taking the correct charge. You need a volt meter and hydrometer to test. What battery is in it? 24 or 36 volt? I f you have one bad cell, the truck wont work. You could have a corroded terminal or post. Same result, no power. The truck need to see a higher voltage than what it had when the battery went dead. If you have a 24 volt battery, it needs to see 25.3 before the truck swings the battery meter to 100%. If 36 volts battery, you need 37.6 before the truck re-sets the battery guage to 100%.
If you can lift, load test the battery by working the lift motor. See how much power is lost while lifting. A 24 volt bat might lose 2-3 volts under load maximun. If you drop to 18 volts, you have a bad cell. You can check each cell with a voltmeter on lift. The bad one will show lower than other cells, like 1 volt or less. Also, after working the truck, a hot battery connection indicates resistance. Remove all caps and look for burned connections. There could be a bad solder.

G'day Raytech and swoop223,
Thank you for your responces, all very helpful. How do i tell if the batterys are bad?? Is there a way of testing the batteries?? The lift has fits and starts, sometimes it will run all day without losing much charge at all - just the regular amount you would expect - it will still self lift while travelling forward or backward as explained in initial post though. Other days it will not work at all, fully charged of the charger it will give 0% charge once the charger is disconected. Confused!!!

and to add to what raytech says
low battery can cause all sorts of electrical problems , all functions in these control panels require a set range of voltage to operate correctly, if it is too low you can get all sorts of strange acting problems.
and yes, as raytech says, you can not diagnose a truck correctly with a faulty or discharged battery.

If your battery wont hold a charge, you cannot diagnose anything. If you continue to run with a bad battery, you will take out the VM