My left prescription is stronger, and its battery usually dies 4-6 hours before the right. Since my batteries last ~4 days with heavy streaming, that means the right has 10-15% of its life remaining when my left dies. But it is not uncommon for my right aid to say 40% when my left dies. Nor is it uncommon for both aids to read 100% after two days of use and 80% at the starts of the day but not last to 5 o’clock. The percentage just isn’t that accurate.
That said, if your aids are significantly different it may indicate a problem. When my right aid started using two batteries for every one my left did, it was because of microphone failure.