Also, if the cars cranking battery is failing, it can scramble the fob. If cranking voltage drops too low, the challenge / response activity with the key does not complete leaving things in a limbo. The key must be replaced and if too many keys are issued, the EIS ( Electronic Ignition Switch , the place that you insert and turn the fob ) replaced unless you get a hold of a china e bay programmer.

I have had cranking batteries that would crank forever but drooped too far under a load. Rather than a 12 V battery they were a 10 due to a shorted cell.