Oldest HV battery? also P3009 & transmission fluid

I'm curious, in general what is the oldest / highest mileage HV battery? Our March 2002 is now over 19 years old with a bit over 276000 miles on it. The HV battery has never been replaced or "serviced".

I had the dreaded red triangle last week and the shop pulled a P3009 code - high voltage leak detected. Subsequently they could not duplicate the issue. One of the things they asked me was whether I had recently had the transmission fluid replaced. I said no. I looked this up, and one site says that a short can occur through old transmission fluid because it can become conductive. (It turns out the shop asked me about this they said because fluid spills could cause the short).

I'd have to look up my service records, but it's probably been 100k miles or more since I had the trans fluid flushed and replaced. So I had them do that. The problem has not repeated in the week since. How likely is it that the trans fluid was really the problem, or can I expect transmission failure or HV battery failure in the near future?

Otherwise it still runs great. I had the inverter coolant pump replaced last year, and the ignition coils and plugs replaced last year as well, but no other big issues.

 

Garage kept since purchase, Colorado (dry climate), 5500' altitude. I watched a DIY video and now I'm curious if the shop removed and cleaned the pan when they flushed it. In the video I saw, there was a lot of sludge in there. I'm mainly curious here whether the P3009 can actually occur because of a short through old transmission fluid.

 

The issue has not recurred. If it does I will try to isolate it.