We see so many dead and un-repairable 3000 and 4000 motherboards due to those damm batteries!!!
When I got my 2nd hand Amiga, the previous owner had swapped out the battery with another barrel one. I ended up ordering a coin battery adapter off of ebay. For some rason the way the pins were, it was harder to get the one from Amikit to fit right.
But since he's selling these and doesn't care about the clock at all, definitely remove the ol' leaky bastards before they have a chance to cause damage.
Odd that the Atari systems all used some weird NVRAM battery block.