Titus, the failure will show as a cascade. First one Gen failure will occur. (lane lamp will come on) If you must fly for a while on only one Gen the other will keep the engine running. If that remaining Gen fails it will turn on the other lane lamp. At this time you need to switch on your battery backup and you should have power for as long as your battery has power, if correctly selected by the OEM that would be about 45 mins run time from that point. Turn off all unnecessary power drains. Most OEM now have the electrical systems with relay switches to turn on the battery power however that is something you need to know depending on your own aircraft design in the electrical system. In some cases you will need to turn on the battery from a switch on your panel.
While it is unlikely you will fail both lanes at the same time one can never assume this is a predictable thing. In some cases in the past few years we have seen people flying on one lane only for prolonged periods of time. If you have a lane light with solid lamp showing you should be landing at your nearest airport and dont carry on as some people have. No need to land in the bush until you have exhausted all your electrical power even in a dual Gen failure. The battery should be good enough to get to a safe landing field.
Cheers
