Counting backpack slots?

[sharpie]

So I'm hunting in an area just mainly getting a bunch of quick, crap loot to sell rather quickly. I have statements within the script to run back to town if I'm low on potions or cap, but I tend to run out of backpack slots before either of these happen. I'm carrying 8 backpacks, and mainly don't use more than that because I use tibia auto to sort the loot into separate backpacks. Is it possible for blackd to count backpack slots at all so when they are all filled I could run back? I've got 5 or 6 years experience with the bot but this one seems to puzzle me :D]
Thanks

Josh