Noah is right.
Last year going into Osh the alternator failed on our plane. Our 9 is equipped with a single Odyssey PC680 that is around 3 years old now. It has been the victom of a master switch that was left on for 3 weeks and then from a charger that didn't' have enough kick to get it charging in the correct polarity. (Somebody told me this isn't uncommon with these types of batteries, but I don't know where.) So after using an old charger on wheels from a service station that hummed when the juice was turned on the battery charged correctly. After about two minutes on that the charger designed for the Odyssey did the trick. In other words this thing was dead, dead, dead. Okay, back to Osh. A friend was flying on my wing and with the distraction I never saw the indication on the panel that my alternator had given up. By the time it was noticed we were only a short distance from Osh so everything that could be turned off was and we continued inbound. Running only the 496 to navigate and taking advantage of its internal battery the only worry was whether or not the electronic ignition would act up, or so I thought. So inbound we continued and as we got close I turned on the number one radio that has no gps to consume power. Right after hearing "Nice wing wag RV, continue behind the Bonanza ahead" my radio started cutting in and out. I powered up the number two and it wouldn't work. It was very busy now, both in the air and turning on the handheld which was out and ready. It was around this point that I discovered that the flaps wouldn't go down with the voltage available, nor would the airplane trim. So there we were on final to Osh with no flaps, badly out of trim with very heavy controls, a hand held being held up to my ear by the passenger, and a plane in front of me and behind me that will all be sharing the same runway at the same time. My mind kept going to my Lightspeed and whether or not it would become an issue which would leave me with only a mag to boot. The lightspeed never gave any indication of any problem. The plane simply ran beautifully! Later after landing and setting up camp I tried to purchase a battery at Osh thinking that this thing should just be trashed after twice being completely dead in its two year life at this point. I purchased a battery from spruce, but it wasn't an Odyssey because they didn't have one, or anybody else for that matter. We walked all over looking for one. Back at the plane we discovered that this battery wouldn't fit into the Odyssey mounting box. Spruce took the battery back and off we went to try and get the Odyssey charged. After about 6 hours on the chargers at the help area at Osh the battery was ready to try. A plane parts alternator was purchased and installed replacing the one that came in my FWF kit from Vans that was well used when I got it. This was my third alternator failure with that alternator with the internal regulator being the weak link. We have been flying the plane for another year now and the battery is strong and reliable. On the coldest winter days in our area that come in around 25 degrees F the prop spins with gusto when the key is turned. These are very hearty batteries indeed. ( I also have a belief that my Lighspeed will continue to run until my fuel is exhausted just as advertised. )
If flying IFR I'd probably replace my battery often also, but this post was just to show the way these Odysseys can bounce back from being horribly abused.
and used one of my RC chargers to bring it back at a very slow rate of charge. I had it a year before flying. 
