you will fry the battery with the lower rating .......
explained as bellow
if you connect the two batteries than nothing will happen at that time , all will happen when you complete the circuit..
now
the bat with 25c will give out the power of approx 250 watts
it means that a total of 32amps of current will be flowing , and the later bat give 90watts means a total of 12amps
when both the batt are connected in parellel than according to kirchoff's law of current the rest of current [32-12=20A]
will be flowing thorugh the low rating battery and this huge current will fry your battery......
its just a guess but results may vary , battery my blast , catch fire , or nothing will happen if my guess is wrong.....
plz reply me your results...