This Hp 6901p battery would appear to only want to give me 4m minutes of juice. Not what I would call long enough. And hence I'd been on ebay to look for another. There was an option to change the 6 cell battery to a 9 cell battery taking the power from 44mAh to 7800mAh. And so I ordered a 9 cell one for 30 quid.
The battery cam so I lifted my laptop up and
undid the clips and slid out the battery.
What became apparnet was the fact that the bigger capacity battery was in fact bigger!
And thus protudes from the back somewhat!
In real life though it is livable with and only comes out as far as the power cord socket.
And now after following the batteries installation instructions of charging and discharging 3 times fully, I get areal 3 and half hours run time just like it says. Brilliant!