How many commercial devices have you seen that can take the battery inserted any way - not many methinks. Digital cameras- the batteries only go in one way, remote controls - same, mobile phones-same. If you look at the battery in your mobile phone it is designed to go in only one way and for good reason. Li Ion batteries have a tendency to go up in flames if treated badly. It is always good practice to have some form of assymetry in order to guide the human - one way it fits, the other it doesn't - there is no half way. The problem with determining the battery polarity is the case where the battery may be flat (ie fully discharged) - how can one determine which way to apply the current in order to charge it? There may be some method of pulsing a current into the battery to see which way one should charge it but I haven't seen it and if you could you'll need extra electronics to determine and cope with the reversal. This will most likely end up more expensive than just a design change to the plastics(or whatever). Remember the design is a one-time cost, every component you add to the product costs each time.

Suggest to the industrial design guys that they should apply good design practices that force the user to do the right thing and thus your problem is solved. Apply KISS (keep it simple-stupid) principle.

Sorry I couldn't give you the answer you wanted but I've had heaps of experience (read mistakes) with human interface issues.