HV battery dying in my '04?

I drove into the dealer for scheduled maintenance on my 2004 with 274K miles. As I waited in my car for the service rep to write up a ticket, the brake (O) and VSC warning lights came on, and also the hybrid system warning on the display panel (red car with ! through it). I'd never seen these lights before, and the car has been driving fine. When they went to drive into the service bay, it wouldn't run so they (said) they had to push it. After 90 minutes and $100 they said it was a variety of codes that pointed to the inverter (a $4000 repair!), but they suggested these symptoms might also be caused by a failing HV battery and could check that out for $400 (!). I wanted to check here to see if this is all reasonable procedure and cost before I give OK for more work.

Since I'm the original owner, and it has the original HV battery, it's more than possible it's at end of life. But I wasn't quite ready to part with it, possibly holding out for the next plug-in model. That said, I've been getting intermittent check engine light due to catalytic converter age, and it does use about 2 qt of oil in 5000 miles. I think in just writing this, I'm convincing myself any battery repair would be throwing good money after bad. Perhaps more important, should I trust this dealership with another Prius purchase and service?

 

The codes were:
P3009 high voltage power short circuit, with info codes: 526 and 612.

Dealer recommends removing hybrid battery to check for terminal corrosion - may need to replace inverter.
Googling those codes, I found they probably indicate a battery problem, but not 100%.

I'm checking with local guys that might take this off my hands. No calls back from salvagers yet. :-( I'm starting to lean toward a dealer trade-in, but only *after* I get a firm price quote from them without the trade-in. Any other suggestions?