Battery problem

Hi,

If I take the battery from my Inspiron 5100 and put it in a Latitude 100L,
it works straight away. However if I take the Latitude battery and put in in
the Inspiron, the Inspiron battery light flashes green and amber in a
repeated sequence, and the laptop won't power on.

Do I need to do something to make the Lat batt work in the Insp or is there
a basic incompatibilty?
By the way the latitude battery works fine in the Latitude!

Thanks,

SW