A car battery can test good and still fail the next cold morning because resting voltage does not show cranking ability. Cold reduces available battery performance while the demand of starting the engine can increase.
A good voltage is not cranking ability
A battery can show acceptable resting voltage yet have inadequate cranking capability. Cold-cranking ability, state of charge, parasitic load and intermittent connections can all produce a confusing result.
Why the next cold morning is different
Cold temperatures reduce available battery performance, and engine starting demand can increase at the same time. A voltage-only result can miss that combination.