My MBA battery just can't seem to keep me satisfied anymore. When new I was getting 4-5 hours. Now the battery is down to about 87-89% and I'm getting 3 1/2 hours tops. I see these batteries "genuine battery for MBA Apple" on eBay for $40-80 and wonder has anybody here bought one? They're definitely not Apple even though they are a genuine battery. 5400 mAh's too. In the past when buying generic batteries I've found there's always something that doesn't quite match Apple spec. Serial number, lights don't, fit on old PB feet... But the MBA batteries are hidden. Any experience at all with generic batteries for the MBA?