Alas poor WP34S

[burkhard]

An open-circuit voltage of 2.7V (on the "new" batteries) is pretty marginal I think.

If the calculator had already been flashed, you could probably run like that (but not long before the Low Battery annunciator comes on), but the flashing operation itself is a bit power-intensive and I suspect the voltage will dip further (too far?) when that load is applied.

I think I'd try again with some new(er) batteries and perhaps a bench supply like the prior commenter recommends. I have doubts that you have killed it.