If you've been flying for years, as I have, you manage to learn some lessons the hard way. I thought I'd share this doozie to help a new piot not repeat the same mistake. I also added an identified lesson learned at the end to help others. I was doing an urgent dog rescue flight where I was meeting the puppy passengers from the kill shelter after a long ride by a volunteer to bring them to me. I had just had my Electro-Air ignition installed and my magneto was swapped out with a recently inspected unit. The plane had flown afterward for a couple of hours without an issue. The flight was to be about two hours and I had to meet another pilot who had already departed to the exchange airport. Passengers arrived, everyone was loaded and on run-up for this flight, there was something that felt off with the magneto. Nothing obvious but something got my attention and I told myself that if anything was off with the magneto that I could just switch if off in an emergency and finish the flight on the amazing electronic ignition. I still love my Electro-Air ignition. About halfway through the flight, the engine started running rough. Switching off the magneto solved the issue. My plan was to finish the rest of the flight on the electronic. Everything was running smoothly. Halfway over the Chesapeake Bay, for the very first time, I lost my alternator and started running down battery power which is kind of needed for the electronic ignition. Apparently the chances of having an electrical failure on this flight was 100%. I diverted to the nearest airport across the Bay and as I reduced RPM in the descent I switched back on the magneto, just in case. It ran rough but the battery was dropping fast. I landed and the pilot I was to meet made the jump to meet me at the new airport. He arrived with a rough running engine. There were only three planes on the ramp that day. A Citation jet, my 182, and the Mooney. All three of us were reaching for and sharing tools. The Mooney pilot opened his cowling and found a loose plug wire. He tightened it, took the puppies and left. The Citation pilot was stuck waiting for a part. I took the battery out and tried to have it charged at a local auto shop. It was so dead it would not take a quick charge. I had to leave the plane and fly home commercially. Turns out my rough magneto was because of a plug wire that had not been entirely tightened. The alternator and battery were replaced. Lesson Learned: A corporate pilot friend said when he has that nagging feeling before a flight he calls a pilot friend. He often found that just by talking it through with another pilot that the go-no-go decision kind of made itself clear. I agree. That would have been the smartest thing to do and if I had phoned a friend to talk it over with I probably never would have departed, to begin with. I never made that same kind of mistake again because even thinking of calling someone, stops me in my tracks. It's hard to say no when so many other moving parts are counting on you but I no longer have that problem.