Q: iPhone 4s wont turn off the screen while on call

Hello there, Aneemax.

The following Knowledge Base article is a great resource for many of the issues you're describing:

iPhone: Hardware troubleshooting

http://support.apple.com/kb/ts2802

Working with the device within acceptable temperatures:

iPhone acceptable temperatures

• iPhone, iPad, and iPod touch (4th generation): Keeping device within acceptable operating temperatures
• Keeping the original iPhone within acceptable temperatures

When the screen doesn't got black during a call:

Screen won't lock or go black when answering calls

1. Verify mute or speaker have not been activated, just prior to placing your ear over the receiver.
2. While on a call hold your hand over the top third of the display, and verify that the screen is locked or goes to sleep.
3. Try turning iPhone off and then on again.

Additionally in regards to battery life, the following article offers some great information as well:

iPhone and iPod touch: Charging the battery

http://support.apple.com/kb/HT1476

In regards to battery life the following article provides some practical information:

About battery life and the battery

Battery life and number of charge cycles vary by use and settings. Find more information about batteries foriPhone and iPod.

Find information on how long the battery is expected to last between charges.

Thanks for reaching out to Apple Support Communities.

Cheers,
Pedro.