Wow, this a throwback to the past. I remember the airport security being very diligent about loose batteries in luggage in the '80s and '90s - some notion of terrorists using them to trigger devices with them mid-flight. But they seemed to have eased off on that over time, and I've never had a problem flying with a few extra AA batteries or other batteries for years. There have not even been concern with portable lithium-ion battery packs which possibly are more dangerous because of the risk of fire. But I haven't flown in India for more than a year now.

Question for OP - did they say the loose batteries would be OK in checked luggage? And what does "installed" mean - are they OK with removable batteries in a device or are they only allowing batteries that are non-removable in devices like smartphones?? If this is new practice it's going to be quite a nuisance to travel with cameras, shavers, etc.