What also concerns me is that the person I spoke to said that the batteries would have been performing poorly at this point anyway. I'm skeptical of this. There was a story recently about a test done on a Prius which found that after 10 years, its batteries were operating at something like 95%. But a Segway's battery goes below 50% after four?
It is my understanding that the Prius deliberately doesn't use all of its battery capacity when new. By that I mean that it tells the user that the battery is empty a fair way before it actually is.
As the batteries degrade it uses more and more capacity, giving the user a consistent experience over time. The Segway doesn't really has this as an option, on something like that you can't be dragging around battery capacity you aren't using.
I'm not sure the Prius actually ever uses more of the battery's "capacity range" as it ages; as I understand it, it's just restricting the charge-discharge to a zone which is less chemically stressful to the battery. You get less capacity, but you get a much, much longer life.
In particular on LiIons, when you go below 2v per cell, that's the point at which most safety circuits just call it a day - forever. Discharge below that point is pretty fatal, with lots of irreversible chemical changes taking place which mean you really don't want to charge them ever again. Charging over about 4v is also bad - that last 0.2v is really stressful, which is why the charge termination tolerances are so tight on LiIon chargers.
If your product has some small discharge (eg to run safety circuits or whatever) and you stop the "product mode" discharge - eg, driving around - at a point where there's still significant battery capacity available (say, 3.5v), you can buy months or even years of time before the battery will get down to 2v. However, if you drain every last drop out (say you stop at 3.0v) then there's actually very little capacity available, and you could be at 2v with a dead pack before you know it.
I'd be a bit worried about "reconditioning" of LiIon packs if they have gone below 2v... ie, I'd be charging the device away from buildings
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