Power Boost Switch

That doesnt sound so bad to me.
If you can check the sides of the batteries with a ruler, commonly they bulge out of one side when they fail.
Presumably you have checked the water levels, assuming they are not sealed cells.
After a run disconnect the battery & check around for hot cables, contactors & control units, its possible there could be a bad connection dropping voltage to the motor slowing it down.
I occasionally maintain Fork lifts and this is fairly common.

The total voltages you measured are too low. Measure the total when still charging but when the battery is fully charged. It should be 38.4V or a little more. If lower then the charger is not fully charging the battery.
Measure each cell when charging but when the battery is fully charged. Each cell should be 12.8V or a little more. You might find only one cell is bad.

audioguru said:

The total voltages you measured are too low. Measure the total when still charging but when the battery is fully charged. It should be 38.4V or a little more. If lower then the charger is not fully charging the battery.
Measure each cell when charging but when the battery is fully charged. Each cell should be 12.8V or a little more. You might find only one cell is bad.

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Am I understanding that you suggest I run the charger, then when it cuts out, unplug it, then plug it back in and start the charger again. When the charger is running again, measure the voltages?

dr pepper said:

That doesnt sound so bad to me.
If you can check the sides of the batteries with a ruler, commonly they bulge out of one side when they fail.
Presumably you have checked the water levels, assuming they are not sealed cells.
After a run disconnect the battery & check around for hot cables, contactors & control units, its possible there could be a bad connection dropping voltage to the motor slowing it down.
I occasionally maintain Fork lifts and this is fairly common.

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Yeah, the batteries do seem to have a slight bulge. Electrolyte levels are fine and I have already replace a couple of leads that were getting warm after a long run.
When I look inside the battery, the plates look like they are quite sulphated. I understand that sulphated batteries may not take full charge.
I have been looking into Auto Pulse Battery Desulfators. Have you any thoughts on these?

Bad news then the plates are sulphated to the point where they are bent by the sounds, thats the point where most would throw in the towel & fit new.

I've looked into sulphators, I read up on how they are sposed to work.
Fork truck batteries cost a lot of money, you'd think if they were a good idea they'd be supplied with a truck or sold by the agents..
Then again battery manufacts wouldnt want that.
So I dont really have any concrete evidence on that one.

You used to be able to get a 'power pill' for lead acids, they gave you a temporary recovery, just enough to trade the machine in working.

Tezzadactyl said:

I have been looking into Auto Pulse Battery Desulfators. Have you any thoughts on these?

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That's what I mentioned in my earlier post (#16), in principle if not by any brand name.

Though if the batteries are starting to bulge, they are likely beyond recovery by any means..

rjenkinsgb said:

That's what I mentioned in my earlier post (#16), in principle if not by any brand name.

Though if the batteries are starting to bulge, they are likely beyond recovery by any means..

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Thanks for the links to that info. That's what got me considering trying one. I have seen some that will work on 12,24,36 or 48 volts. They are not too expensive so I might get one and leave it connected all the time and see if the numbers improve.