Settings that drain battery the most, in the order of severity:
1. Google auto-Sync. If you leave your phone to sync at all times (say, you're expecting an important urgent email) this will eat your battery like a pig. Plus your data, which is a separate subject. Also if you have widgets that display weather - change settings to manual. I use xWidgets, it's very easy to update weather manually when I need to. And for email, use Type Mail - the widget has little circle where you tap to check for new mail. Don't forget to set to manual within the app, though. You can always ask the team for help.
2. Location & GPS. They eat battery like crazy, and this is why I don't bother installing tracking apps. I will have to enable GPS all the time, loosing charge, only for the sake of hoping to find my phone if someone steals it? And the chances are small to have it back if someone steals it. So, I better keep my eye on my device, not leaving it in the open and not snapping my mouth. Location can be quickly enabled if you need to use maps or GPS, and then disable it right away.
3. Bluetooth. I noticed on many people's devices (many folks come to me at work with questions since I know things, this is how I see their devices) bluetooth enabled all the time. I asked them "Why do you have it on?" - they have no answer. Watch for the green symbol in your notification pannel, you only need bluetooth on when you need it, otherwise turn it off.
4. Screen auto-rotate. This uses battery as well, as it keeps the gravity sensor alive. Some people like auto-rotation, so it's probably ok to sacrifice a bit of battery. After all, if all you do is saving-saving-saving, why having device at all if you aren't enjoying it? But I personally can't stand this auto-rotation, so I keep it always off.
And if all of these still doesn't help and your battery is being drained quickly, there are 2 options:
1. Your battery is old. If you have your phone for about 2 years or more, don't be surprised. Batteries are made today to be charged-discharged about 500 times - and it's true for good quality batteries, like Samsung.
2. You may have some form of spyware iin your phone, or some junky app is eating your battery. I suggest in this case to restore phone to factory settings and have a new start. Don't forget to back up all your contacts to Google account before doing restore! In this case, you need to enable Google sync, yes, it's worth it.
There are after-market extended batteries. I can recommend Anker. It is a great company, with fantastic customer support. I bought extended battery through Amazon, and now I charge my Samsung Galaxy SIII only once in 3 days.
All the best!
@Martin that's exactly it!
In addition, lithium-ion batteries have an optimal operating temperature as well. I think it is around 20c.
All electric cars and plug-in hybrids operate under the same principle. That is, even though the dashboard says the battery is fully drained, it is not really so because of what Martin pointed out. Similarly, when the car is fully charged, it is not really fully 100% charged. This is done to maximize battery longevity. So you may sometimes see a plugin hybrid that says it has an 18KWh battery of which only 14KWh is useable.
You may have heard of premature battery degredation in early model years of the Nissan Leaf. This was due to inadequate cooling of the battery during high charge rates resulting in the battery overheating. Also, not really a problem, but there have been reports of Leafs not allowed to be driven in -20c weather because the battery was too cold. They had to wait 10 minutes for the battery to warm before they could move.
So temperature definitely has an impact on the battery as well.
"One of the main things to avoid from what I heard is to keep the phone on charge during night. Those 8 hours of sleep without unolugging it will damage the battery as it remains unused for ~5 hours on the plug.
It drains the durability pretty quickly."
This is controversial advice. And it apparently varies with the differing electrochemistries and material qualities of different lithium-ion battery designs. Remember that one of the main parameters the "battery engineers" have to consider is price - many cellphones use less advanced battery technologies because they want to keep total price-per-unit attractive to the end consumer. (Even on premium smartphones - which is why the manufacturer often sells the phone with a "standard" battery model while also offering a "better" battery model for added cost.)
The main killer for lithium-ion batteries is simulataneous charge and discharge, it increases internal temperature and changes the chemical equilibrium thresholds, so anodes and cathodes degrade faster and electrolytics saturate faster and secondary chemical products gas off (leak/vent) faster. End result is that a hot battery will hold high charge for months instead of years. Today's lithium-ions seem to last longest (that is, they hold more of their maximum charge longer and discharge slower) when regularly topped up to full charge and never/rarely allowed to completely discharge "into the red". Disabling power-consuming features (like cellular/bluetooth/GPS transmissions, heavy CPU burdens, etc, as described above) minimizes battery discharge, especially important when charging the battery near its rated temperature extremes.
Sorry for sticking in, but knowing that to some folks this sentence might sound like Chinese, I just want to interpret into simpler language "The main killer for lithium-ion batteries is simulataneous charge and discharge, it increases internal temperature and changes the chemical equilibrium thresholds, so anodes and cathodes degrade faster and electrolytics saturate faster and secondary chemical products gas off (leak/vent) faster."
In other words, when you are using your phone and charging it at the same time, this is not good for your battery. The best thing to do is to disable most functionalities, and even better to turn phone off during charge. Of course, since this usually isn't an option, try at least to not use phone while it's charging.
It can be compared to us eating - you don't want to exercise while eating, do you? Like, there is time to work hard and there is time to relax and eat (i.e. charge our stomachs). Otherwise what would happen? You will screw up your "chemical equilibrium thresholds" and then your secondary products will, so to speak, gas off too much. Same thing is true for your phone. If we give our phone a stomach (battery) ache too often, it will give up and say "I quit".
Hope it helps more people to understand the meaning behind the science :-)
Another tip which sounds counter intuitive is do not let a Lithium Ion battery completely discharge.
This is even worse if you are storing it (eg upgrade and put old phone in box)
Most Lithium battery's last longer with CONSTANT charging
Some companies even recomend storing batteries in a charger if not in use
One of the things that drains a huge amount of data that most people do not realize is programs such as email that are set to a high frequency update check, or even apps such as facebook.
It is good to set higher update frequencies and manually check when you go on your phone.