The mod in question was to replace the button-cell battery in the Dreamcast with a Ni-MH rechargeable AA, since I don't know of anyone who still kept their Dreamcast and that intact. I also think it was stupid how the thing only charges when the system is on (instead of as long as it's plugged in like the PS2 and every other system since).
And yea, I really wish the VMU's had room for a standard battery, or that there was such a thing as a rechargeable CR2032 battery. --
Because, f*ck Sony