I have digital camera, am wondering why it keeps on saying to change the batteries when I've already done it.

Its better to use rechargable lithium batteries. I bought a charger with 4 batteries included from Currys and find that they last much longer than disposables. Its always good to have at least 2 pairs of rechargables with you so you can change over if one goes flat. Either way, Digital Cameras will always be hard on batteries! Sad....but true.

To cover all bases, are you sure you are using new batteries as replacement? They may not be "fresh" batteries, and therefore may have drained through the years.

Alternatively, you may have a problem with the camera itself.

If you're using AA size batteries make sure you've got the right kind. Normal AA batteries have about 1500mAh. Cameras require more juice than that. Try 2100mAh (or higher), or make sure the package clearly states that they're okay for cameras.

Digital cameras need real powerful batteries, try original Duracell batteries.