On the two weeks that I have been tinkering with my phone, I noticed that there were several factors that considerably affected its battery life. There were times that after 2 days the battery has less than 25% charge left in it, and there were times that a day has finished and only less than 10% of the charge has been used. I tried several settings from within the phone and came up with a list that could help everyone extend the phone’s battery life:
1. Turn off 3G if you’re not using it or if you don’t expect anyone placing a video call to you. You can do so through Settings|Connectivity|Mobile Networks|GSM/3G Networks and selecting GSM only. This stops your phone from searching for 3G signals, which may be good in some countries like the Philippines, wherein 3G signals are still spotty at quite a lot of places.
2. Set the brightness to the lowest setting. I found out that although a bit small compared to those from other phones, the LCD screen of the K800i is very bright. Out of the box the phone has it set to the highest, which is 100% brightness. If you seldom use the phone outdoors, you can just set the birghtness level to 50%, which is still very much readable indors. Go to Settings|Display|Brightness and then move the the joystick to the left several times so that all the bars shown are all white, then select Save.
3. Avoid using themes that have a light background. The darker a theme is, the lower the power it takes for the LCD to display the wallpaper, icons, etc. Go to Settings|Display|Themes and select the theme of your choice.
4. Avoid using animated wallpapers. They may look cute, but eventually the novelty wears off. and besides, the animation takes its toll on the LCD screen, causing it to consume more battery charge like that when you use light color-based themes. Go to Settings|Display|Wallpaper to change the wallpaper shown when the phone is idle.
5. Use short, yet loud ringtones and message tones. A short message tone (like a breaking glass sound effect) will take less time for the speakers to be utilized, but can definitely get your attention. Same goes true with that of the ringtone. Go to either Settings|Sounds & alerts|Ringtone or Settings|Sounds & alerts|Message alert to change things.
6. A variation to the previous item is to set the Increasing ring option to On. This starts the ringtone at a low volume, and then gradually increasing the level of the volume as the ringtone is being played. This way, you can still use that annoying Crazy Frog ringtone without taking too much battery life. Go to Settings|Sounds & alerts|Increasing ring.
7. Use the profiles! The default Normal profile can fairly be suitable, provided you have good ringtones (those that can easily get your attention). However when indoors, you can change the setting to make the sound play a bit softer by selecting one that is set to a lower volume level. Make a short press to the power button, and then select one from the available profiles. The ring volume, as well as the vibration settings are then changed to what is saved in the profile. Bear in mind that these can be modified as you wish. Go to Settings|General|Profiles, select More to display a submenu, then select View and edit to either view or change the current settings for a profile.
8. Turn off vibration. I guess this isn’t needed when you’re at your desk and the phone is laid on the table. Go to Settings|Sounds & alerts|Vibrating alert and change it to On if in Silent. This way, the phone will only vibrate when you switch to Silent mode (that is when you press and hold the # key of the phone).
9. Do not use the sleep mode clock. After some time the phone turns off its LCD to conserve battery life. There is an option where a clock is displayed during this power saving mode. If this has been set, you can turn this off by going to Settings|Display|Sleep mode clock.
10. Do not use the screen saver. The phone has an option wherein after a few seconds of being idle it would display an image. You can turn it off through Settings|Display|Screen saver.
Now, given that I use the phone to make calls, send short messages, take pictures, and play music, the longest time I could eke out from the phone is a little over 4 days. Rarely do I ever have to charge the phone after 24 hours. On the average I charge the phone after three full days (with around 25% battery charge remaining) — receiving several calls, sending/receiving 25-50 SMS messages, and about 1 hour listening to podcasts per day. Manufacturers recommend that Lithium-Polymer batteries are not to be fully drained of its charge.
I hope these suggestions can help others as much as it helped me.