How to troubleshoot/debug slow phone that burns battery? My phone is a Samsung Galaxy S5 mini, so it's getting old by industry standards. Until a few months ago, it was doing fine, but recently the battery life and response time have drastically degraded. Even with every optimisation I know of, I am now lucky if the battery lasts a day (~16h). 8h is more typical. The phone sometimes hangs for long enough for the screen lock to activate (2 minutes). When the hanging is particularly bad, I have noticed that the phone feels warm.

I have seen messages saying that two apps (Facebook messenger and DJI pilot) have caused ~17 errors each in the past week, so I should optimize power settings. Activating "save power" hasn't helped.

The standard battery indicator says that 20-25% is used by the screen , 15-20% by the Android System, and 10-15% by Android OS. I tried to get more information on the battery by installing "Repair Battery Life". This app claimed to repair 5 "low" cells. But it seemed far too easy. I'm sceptical whether an app can repair battery cells.

I can think of some things that have changed in the last few months, but I wouldn't expect them to have made such a big difference. I have installed some new apps, but none use more than 3% of battery. I assume this means that they're not consuming enough CPU to hang the phone either. One of the new apps is perhaps more of a suspect than the others: Netguard. I would expect that less network traffic would save battery, but I could be mistaken if apps are very aggressive about retrying the connection. Finally, I have moved house, and the reception (wifi &amp; whatever you call the normal network) might be worse, but not noticeably.

What else can I try to get more information on the problem(s)?

Update: I noticed two new symptoms.

1) the phone only seems to hang when I am out of wifi range.

2) looking closer at the battery menu under Settings, there seems to be significant battery usage at times where the phone is "awake" but the screen is off. Does this mean that some app is constantly waking the CPU?

Update2: today I had the screen on for 2 hours straight, which took my battery from ~75% to 15%. Clearly, a lot of this was for the screen, so I was surprised to see that in the battery stats, it says that the screen used 15% of the battery, while "android system" used much more: 19% and 5 hours of CPU time. "Android OS" also has a significant contribution with 8%. Is there any way to narrow down why the Android components are so active?
Educated guess is you have apps that are running in the background and eating up your battery. Samsung power manager app/thing is not great (at least on my sgs7 it isn't), but it's pointing you on possible culprits. Easiest way to debug is uninstall the apps and see if device acts any differently (give it a few days or a week to see). Or another way is factory reset start from new and see how it goes from "stock" and add apps slowly and see. Or it could just be the battery is aging and simply can't hold a charge like it used to. There isn't a silver bullet way of trouble shoot battery life unfortunately.