Weird, because I've got 3 and non of them have shown and signs whatsoever of giving up yet, even the one in my Wheely King, which gets thrashed, crashed and bashed about a *lot*. I don't expect them to last forever but they seem fine so far. It's all about the torque with crawling anyway, what does the JR9000 throw out?
The system is currently set at 5.8V and is fine, but I can probably push it higher I'd have hoped.