Not sure if this will be of much help but several years ago I was running a warehouse where we had a fleet of Order Pickers (all bought at the same time, all ran roughly the same hours).
One decided to stop raising the cab and the "advice" I got was that the battery was cooked...okay, get a new battery, install it..same issue. Advice was...Oh, it must need charging (Hmmm, brand new battery and it needs charging???) Okay, so it was charged over a 24 hour period...no change!!
3 engineers on-site, crawling over the machine, eventually discovered the lifting chains had stretched and were not making correct contact (or something like that), new chains etc fitted and all was good (including the supposedly cooked battery).
Just a thought.