Solution:

It is a common observation that starting a car engine is more difficult on a cold day due to several factors including increased viscosity of engine oil and reduced battery performance. So, Assertion (A) is true. On a cold day, the chemical reactions inside a battery slow down, leading to an increase in its internal resistance and a decrease in its effective capacity, rather than an increase in EMF. The EMF generally tends to slightly decrease or remain similar. So, Reason (R) is false.