Interstate Golf Cart batteries, which line is best deal?

Hoping mine last. I have the newer costco version. Last camping trip i was a little surprised by my voltage readings. Seemed a bit low. I dont really like that they are the generator starting battery. Already low and then you blast it with a huge load.

Would like to monitor amp draw. Whats the cheapest way to do it these days? I like to solder if you can build your own unit for cheap. Suppose its a google search away. Still fun asking here and gaining knowledge.