How to tell when airbags need to be replaced?

I recently purchased a tri axle dump truck, currently still waiting to get it on the road just doing little things here and there. I’m having an issue where if the lift axle is up and the truck is aired up (120 or so) within 2-3 hours the axle is lowered and the primary air is usually between 90 and 60 or less psi. I’ve been trying to track down the leak but haven’t had much luck, if it’s losing that much pressure I feel as if it would be a fairly noticeable leak, and you’d be able to hear it. I’m starting to think possibly the bags? See attached photo. I know it could be 1,000 different things but if it’s losing that much pressure that quickly surly it should be noticeable?

 

When the axle is up I can’t hear anything from the bags, although I do have a leak in the cab for the pressure regulator and the switch for the lift axle, but again only when the axle is down I can hear it. but lower the axle and I can hear this, I can’t tell if it’s coming from the bags, or something else. It’s hard to tell without lifting the box, and my box prop is very janky and I do not want to be under there! Not sure if this link will work but here’s the leak with the axle down.
https://photos.app.goo.gl/tfojhvghDywQrtdu7

 

This is going to sound like a dumb question, but what exactly do you mean inflate them to max height? I’m not sure how you do that with a lift axle?

 

Yeah the bags do look fairly new, and I know those aren’t the bags that raise the axle. But the bags look squished when the axle is down, and they don’t really look right to me, but maybe that’s how they are supposed to be. I’ll have to try using the prop, it just looks very flimsy and not sure how trustworthy it is. I may have to get some blocks and do that in the future. Why would the air leak only be noticeable when the axle is down but not up? I will have to check and look for that solenoid.