D800, D810 battery compatability ?

Are the batteries for the Latitude D800 and D810 notebooks compatable ?

I have a spare battery I used with my D800 (type Y0956, 11.1V 7050mAH, Dell LBL P/N G2055 A00)

I may have to buy a D810 now to get the RS232 serial port availability.

I have not exactly seen anything that says that they are
but I believe they may be interchangable.

BTW, are there ANY new Dell notebooks with RS-232 ports ? Or is that all totaly gone away now?

thanks,
boB