Jon,
I have the Turbo 3, so am familiar with the general system, though the newer Quantum battery packs are Lithium battery based. You've acertained, correctly, I think the problem, which is that the batteries have lost any kind of conditioning from lack of use -- a significant problem with NiMH batteries. Because of it's construction, there really is no way for you, the user, to check the condition fo the battery. My recommendation is send it to Quantum for evaluation (even if it cost you a little something, since you got the battery for free). Based on their assessment, either have then do a battery replacement with fresh cells, or go with some of the newer battery packs on the market -- most of which are cheaper than Quantum units. Nissen and Bolt produce some nice packs, and Quantum even has more affordable units. It all depends on what Quantum says they will chareg to replace your cells and whether it is worth the cost versus a newer unit. Have it evaluated soon if your shoot is in October.
Nemo