Last month, approaching the Sea of Finland, when suddenly the 'low volt' light came on. No amount of resetting the 'Alt' would restore charging (OK, you should only try that once!). Not fancying the sea crossing to Helsinki without electrics, I made a quick explanation to Sweden control which brought a sympathetic response.
They asked for my mobile no. in case of radio failure and agreed to my turning off the xpndr despite being very close to Arlanda airport. This left just the 430 running, which it did for at least 30 mins. Fortunately I had mugged up on Stockholm Bromma and got direct vectors accordingly. Just before landing the power came back on!
Conclusions: Always revise on possible alternates in foreign countries. Radios will go on working for some time, maybe hours. Turn everything else off. Don't rely on emergency hand held radios - I was carrying one and it was inaudible to the tower. Mobile phone is a far better bet, at low level anyway. Thanks, Sweden control. Oh, and be sure to have a friend already booked on a commercial flight to your destination who can bring a spare alternator in his hand luggage!