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Gentlemen, We have had the HighLowVolt light on the annunciator panel flashing transiently in flight in the past few days. This is the sequence of events: 1. The ammeter showed negative (discharging) on the ground even at 2000rpm. The output of the Volt.Reg. was very low. A new Volt.Reg. didn't solve the problem. 2. An (assumed) wrong grounding wire was removed under the dash and the voltage to the alternator became 9v and the ammeter started showing about +35. We thought the problem was fixed. 3. During the first couple of hours of flying, the ammeter slowly reduced to (and stayed at) about +15, and the HighLowVolt light transiently flashed during flight. We also noticed the lights on the autopilot (the HDG) was very dim during the flight. But it was back to normal when close to the ground for landing. It is normal on the ground. 4. We shutdown the engine on the ground and started again and ran the engine at different configurations, on the ground, including cruise config. No HighLowVolt flashing or dimming was observed. 5. We did another flight. On the ground everything was ok. At around 700 feet AGL, the HighLowVolt started showing transient flashing again. The flashing happens for about a couple of seconds, then it's off, and after about 10 seconds, it shows again. There is no exact timing of the flashing though. But it happens at altitude only. The only difference to me seems the air pressure at altitude that is different from the ground operation. Here is the list of what I think may be wrong. 1. The battery is broken. Does the air pressure affect the battery? 2. The alternator is broken? Can it show the problem in low pressure air only? 3. The connections of the battery need cleaning/replacement? Why is it only affected at altitude? Any other thoughts? p.s. I'm going to connect a multimeter to the cigarette lighter in the next flight tomorrow and observe the voltage during the whole operation.