On Google’s battery optimisation app , it learns and redirects the battery power to the most used user apps and shuts or pauses the battery usage on lesser apps. It does this so background running apps aren’t exhausting battery power.
Your iPhone is good at managing the battery, but it isn’t human. It doesn’t necessarily know when an application really shouldn’t be using the battery when it is any way.
What this means is, there might be an app running in the background checking the weather every 5 minutes. That is takes battery power. Do you really need to know the weather conditions every 5 minutes? Wouldn’t every 30 minutes or even every hour be good enough?
Another example is , Facebook wants to keep you updated right up to the minute. To do this it has to continually monitor your feed and alert you when someone posts or comments. That really sucks down the battery.
An app can give you information about how much battery power these apps are using but the app itself isn’t going to make your battery last any longer. You have to do that yourself (and if you apply a little common sense, you can do it without using a battery app).