Deanna's experience is an important cautionary tale. The basic answer is you don't really know. If a battery costs $50 it's likely to be made out of lower-quality battery cells, assembled less carefully, and have inferior battery electronics. If the battery explodes or otherwise damages your computer, it may make it harder to get ThinkPad protection (although we've had no incidents of this happening to my knowledge.)
You may be able to find a non-OEM battery that is quality made and saves you money from the Lenovo battery, but you'd have to know a lot about the battery manufacturer to feel good about it. I wouldn't even consider a battery without a one year warranty, for instance. The Lenovo battery will come with a new one year warranty and you are guaranteed it will be supported if anything goes wrong with it and damages your computer. And $95 seems a very competitive price for the Lenovo battery from what I've seen. BTW, we have no problem with you buying an official Lenovo battery from somewhere else for less money--we're not making any money off of these, just directly passing on our pricing.