If mains (utility) power is supplied to the box, then it shoudl trickle charge the batteries.
leave it connected for a couple of hours, then fire it up.
If it eventually expired uncontrolled from lack of battery power, then the system may be in an uncontrolled state, and you will have to use the front panel to manage its start up. It involves pressing buttons and arcane knowledge of 2 digit state codes – all in a manual somewhere, but its years since I had to do that.
If it doesn’t power up then, why not call IBM and get explicit details from them? – you *are* on support? – That’s what you pay them for…