Bear in mind NiCads have not been available for some time now, so anyone selling them will probably be selling v.old NiCads which will have deterioated over time.

Think about why someone might be selling their NiCads as well - is it to save weight (like when we sold ours) or is it because they're getting a bit old and beyond their useful life ?

My honest suggestion is NiMh or if not A123's