The issues are separate - the battery will need to be replaced.
So, seemingly will the hard drive - run a full diagnostic on it (F12 at powerup - the EXTENDED test, not just the quick one). 

It seems you have multiple issues with this computer, have you always had these issues?

For the slow performance, computers are usually a bit slower after a system restore. That's normal. But if it's extremely slow you might want to run a Hardware Diagnostics by pressing F12 at the Dell Logo screen on startup.  Choose diagnostics, or Pre-boot System Assessment. Check if it will pass.

As for the battery, pressing F2 at the Dell Logo screen and entering BIOS. Look for battery Health and Battery Info and check the status of the battery. Dell batteries only have a warranty of 1 year. Their batteries degrade after a year so if BIOS shows battery needs to be replaced, you might need to purchase a new one.

0x0000007A: KERNEL_DATA_INPAGE_ERROR
A page of kernel data was not found in the pagefile and could not be read into memory. This might be due to incompatible disk or controller drivers, firmware, or hardware.

http://xps-resource.blogspot.com

No i havent always had these issues.  Ive known about the battery for a couple of weeks, as i keep getting messages about the battery life. 

I did the diagnostics check and got the following error codes; 3600: 0123 and 3600:0749 to do with the battery, and IB63: ICIB and IB63:16IB.  Everything else seemed fine.

Most likely, yes -- the hard drive has developed bad sectors and must be replaced.

Thanks for your reply.

Are these easy to replace yourself or will i have to take it somewhere to be fixed.

Also can you recomend a hard drive and website to buy from?

many thanks

The drive is physically easy to replace:

http://support.dell.com/support/edocs/systems/ins1525/en/SM/hdd.htm#wp1180023

newegg.com is a top-notch vendor.