Lost comms question.

Recently had a battery and alternator failure in flight, PA28RT. Curiously, ammeter appeared to indicate charging current, and checked out ok at preflight.

VFR day xc. After departure, first indication was the GNS530 reboot; then I could hear radio traffic but could not transmit. Then the 530 went down and did not come back, but Com2 (SL30) stayed on; again could hear but not transmit. I then noticed the TC had a nonop flag. I powered down all lights and doubled checked nonessential electrical loads off. About 25min from home base.

While looking at divert options, I squawked 7600 and texted my CFI who happened to be in the hangar. He went up to the tower and they told him ATC had already told them I was inbound (!) and so they cleared me in. Some excitement on approach on whether the gear was down (greens did not illuminate) but CFI confirmed visually by text.

In this case I had multiple people trying to help and for that I am thankful, plus low enough for texts to work.

How did ATC know where I was headed?
 
They can see you on primary radar. Same way I managed to get an Arrow into IAD with only a receiver.

I've found my autopilot starts doing wierd pitch oscillations on low battery. Either I missed turning on the alternator or it tripped (I have breaker/switches).
 
Guess this is a good reason to have foreflight on board- to see what winds are if you don't have a panel mount.

Basically my thoughts are choose the approach to the runway that is wind favorable based on current info either from a panel mount weather device (i.e. My trip page on my Avidyne mfd) or info gathered from foreflight squawk 7600, and fly the approach. Try to keep as close to ETA on exiting last VOR if possible but aviate first.
 
The factory Piper charging instrument set up on the PA-28 is lacking. The ammeter just shows output from the alternator. Add a voltmeter so the system health can be monitored. I use a cheapo voltmeter that plugs into the cigar lighter.
 
I used to have KX-155's. Your low voltage indication is the segments disappearing from the display. The JPI will give low voltage alerts if you program it right.
 
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