A new battery usually helps but even a brand new battery can still give poor performance in cold weather.
Err 2 is as stated before the second sensor not seeing the projectile, first check alignment, second clean the lens! I have found lead dust settling makes the sensors rather less sensitive no matter what light or battery condition.
I only ever bother with my Chrony when I need a downrange velocity to assess BC of a pellet, it can be a royal pain to get a reading when shooting from a distance even with a rested gun carefully sighted against a target behind the Chrony.