Gen 2 Prius won't go to ready after new aux battery.

I have a 2nd gen 2009 Prius T Spirit which I have owned
from new and which has now done 205k miles without any
real issues. The car was stationary for nearly 4 weeks and
when I came to move it the electrics were dead. I checked
the aux 12v battery which was dead showing 3 volts. I
replaced the battery but now the car will not go to Ready
and all the warning lights stay on i.e. VSC, ABS, engine etc
and red triangle (of doom?).
I'm stuck on the drive and loathed to call for garage/AA etc
if it's potentially something I can deal with. Any ideas
welcomed with thanks.