This could be from a variety issues. One being that they are such low mileage means they are rarely ever driven meaning the battery would not have the charging done frequently enough to keep the system topped up. Same reason why we disconnect the battery when we are storing our cars for 5-6 months of time.
with onzedge though I am no aware of any electrical issues with any of the z34's let alone 2010's.
IMO if you find one that's a good deal, jump on it!