Dear Ben (and the community),
I noticed there is some confusion that Ben Heckendorn has been having with the Dreamcast. Like many Arcadian predecessors, and the original XBox the Dreamcast has an on-board battery that can be replaced with a coin cell holder. The reason why I am mentioning it is because like in Arcade machines, and the original XBox... The Dreamcast was designed not to keep time when power is unplugged from the system, but it is however designed to keep time as long as the power is connected and the battery allows it to do so. That being said with constant unplugging (and age of the battery) it can discharge to extinction of the console itself. The reason why I say the console itself is because this type of battery has a design flaw, and leaks over time because of age and constant discharging there by ruining the circuit board. I suggest you look at LukeMorse1's Youtube channel for Arcade machine, and the original XBox mods to the battery circuit to see how to add a coin cell battery holder to your Sega Dreamcast.