I was once told by an instructor that while bringing back a 22, the alt light came on. However the flight time was still around an hour. He flew the hour back with no problems but recommended not doing it again.
Robinson does not say how long his battery's will last, but as a few of you pointed out ' land as soon as pratical' is the wisest option.
The Tachs will still work as long as the clutch is engaged and there is life in the battery due to the tachs running off a seperate circuit.
