Re: my iPhone 4 is losing it's charge every day. can it be repaired or do I have to buy a new phone?
If you are at all mechanically inclined, you can buy a battery and install kit from iFixit.com . They also have videos showing how to do the changeout. Or, if you're in a large city, there are some aftermarket stores that can change the battery for you, at a nominal fee.
The iPhone 4 is quickly becoming outdated if you need to download any data; however, if the main purpose is as a PHONE, the battery swap is the cheapest solution if you want to stick with an Apple product. You might also check out trading up to a refurbished 4s model, as Apple will be supporting that for another year with the release of iOS 9 this fall.