With Microsoft's new Instaload technology, it no longer matters which way you insert the batteries in the enabled devise. Each battery slot has both contacts at both ends. That means it does not matter which side the positive and negative is. No more trying to find the little plus or minus, no more flipping batteries back and forth trying to figure out if you got it wrong or if the batteries are duds; no muss, no fuss, just throw them in however you like and get back to work using them. You can see the official produce page at http://www.microsoft.com/hardware/mouseandkeyboard/licensing/instaloadoverview.mspx.
Some of the commentators have expressed concern/disappointment/apprehension that it is Microsoft who developed this. The reason is fear of high and/or complicated licensing costs. If they are right you may not see this technology on cheap non-Microsoft devises for a while.
"Microsoft has come up with an amazingly obvious tweak to battery tech that should save us some headaches, as well as several trillion hours of head-scratching and peering into dark holes.
Named Instaload, the invention lets you stuff the batteries into a device any which-way you fancy, eliminating the need to read dark directional diagrams. The most impressive part is the low-tech way this is handled. Each contact in the battery compartment has both positive and negative terminals. If the fat, flat end of the battery is pressing against them, it touches the outside contact. If it is the pointy positive end then it makes contact with a slightly recessed inner contact. This, combined with some simple circuitry, makes sure the current is always running the right way."