What kind of lighting is it?  eg

Escape route lighting
Open area emergency lighting
High-risk task area lighting
Standby lighting

I think the standard you need is  Particular requirements - Luminaires for emergency lighting (IEC 60598-2-22:2021)

I do not have a current copy to hand here, but more generally I note that the sophistication  of LED indicators varies widely between makers.

In some cases it is just a "mains on" indicator, always on when there is a mains supply,  in other cases there is electronics that checks the battery voltage has reached some level that indicates it is charged, and in others yet more complex still with a micro controller that monitors the battery internal resistance by periodically pulsing a load and looking at the droop (a baby DC version of the familiar  Zs test if you like) and these models seem able to indicate many fault states with flashing lights of different pulse patterns or colours.

I am not sure of the minimum required by  standard,  but clearly in a bid to differentiate, various makers go  above and beyond with red lights, green lights and in one very annoying model a selection of beeps and chirps - none of which appear to be harmonised.

I am not aware of a proper emergency light that does not have provision for some sort of 'on charge' indication, and it certainly was a thing in the older versions of the standards for fittings with the battery built in (but not all battery backed up lights are actually emergency lights -as note above.)

.

Mike

I think the standard you need is  Particular requirements - Luminaires for emergency lighting (IEC 60598-2-22:2021)

I do not have a current copy to hand here, but more generally I note that the sophistication  of LED indicators varies widely between makers.

In some cases it is just a "mains on" indicator, always on when there is a mains supply,  in other cases there is electronics that checks the battery voltage has reached some level that indicates it is charged, and in others yet more complex still with a micro controller that monitors the battery internal resistance by periodically pulsing a load and looking at the droop (a baby DC version of the familiar  Zs test if you like) and these models seem able to indicate many fault states with flashing lights of different pulse patterns or colours.

I am not sure of the minimum required by  standard,  but clearly in a bid to differentiate, various makers go  above and beyond with red lights, green lights and in one very annoying model a selection of beeps and chirps - none of which appear to be harmonised.

I am not aware of a proper emergency light that does not have provision for some sort of 'on charge' indication, and it certainly was a thing in the older versions of the standards for fittings with the battery built in (but not all battery backed up lights are actually emergency lights -as note above.)

.

Mike