Something we've noticed with both the HTC One M9 and the Samsung Galaxy S6 is that their battery life isn't all that great. While it'll likely get you through the day - that depends on your usage however. There are a few things you can do to improve the battery life. We've already went over how to improve battery life on the Samsung Galaxy S6, now it's the HTC One M9's turn.
This is a tip I also used with the Galaxy S6. If you are one that is always in and out of the house, then you'll want to keep the brightness on Auto. This does a couple of things. It makes your life easier because you can use your phone outdoors and inside without it being too dark or too bright. Without you needing to change it every time you go outside or back inside. it also saves battery life, compared to you turning the brightness way up when you're outside.
Sometimes you'll come across a rogue app or two. This is why it's a good idea to check your battery stats every once in a while. Sometimes, I'll notice that Chrome or even Twitter will be chewing up a lot of battery when they haven't been used. So it's good to check and see what's chewing up your battery and stop it.
Unlike the Samsung Galaxy S6, the HTC One M9 does not have Qi Wireless Charging. Okay, so what. It does however use Qualcomm's Quick Charge 2.0. So make sure you pick up a Quick Charger for the HTC One M9. We recently just did a top 10 of the best Quick Charge chargers out there. So check those out.
External Battery Packs
The HTC One M9's battery isn't removable. So you can't just pop out the 2800mAh battery and toss in another one. However, you can pick up a battery pack to charge it up throughout the day if needed. There are many external battery packs out there, ranging from about 1,500mAh all the way up to 50,000mAh.
Use Extreme Power Saving Mode
Running low on battery and no where near an outlet to charge it? No problem. HTC has what they call "Extreme Power Saving Mode". This pretty much turns off everything on your phone, so it can last as long as possible. So you can make that last 10% last as long as you need it too.