I drive 2010 Hyundia i30. I recently had my battery flat out after I did not use it for 3 months. The mechanic who helped with the battery situation suggested that I can keep one of the battery leads disconnected if I am not planning to drive the vehicle for more than a week. There is generally nothing unsafe in this IMO but last time my batter was disconnected, the dashboard started showing "ESP OFF" (Electronic Stability Programme) sign. I am not sure what harm that does but car drove ok with that sign on.
Is there any harm in keeping one lead of batter disconnected?