In buildings where there is no electric backup power coming from generators, both emergency and exit lighting run on batteries using it as the secondary power source. Therefore each fixture is supposed to have battery that is capable of running the sign or light in a continuous way. As has been said already the stipulated time in this case 90 minutes. It is also essential that the batteries never fail in this time. So, this can be called a key component of emergency exit lights testing.
As per rules, each and every fixture is supposed to have a battery charger. All the rules and regulations pertaining to manufacturer’s maintenance, requirements of fire codes, and testing instructions are determined as per the 2009 version of National Fire Protection Association Standard 101, Life Safety Code, Articles 18.104.22.168 and 22.214.171.124.1 for emergency lighting.