To check your battery usage in your iPhone, go to Settings > Battery. You'll see this;

The percentages shown are a measurement of how much the app has used of your battery usage for that period (it shows one day and ten days).

So, let's say you start the day on 100% battery. Over the day, your battery may drop to 50%. The percentage Battery Usage By App measure in the settings is a percentage of that 50% (not 100%). So if my battery was at 50%, then 2% usage by the app is actually showing 2% of that 50% (not 100%), so in other words 1% of 100%.

If you then click on the Show Activity tab, it will show you what the app has been doing over that period.

In this case we can see that the app has only been 'open' for 3 minutes, and running in the background for 22 hours and 52 minutes.

If you feel that Aglet is using 'too much' of your battery, compare these two measures against another app you're using. You will probably discover that other apps are actually far more resource intensive than Aglet.