Im afraid your provider is spinning you a tale.
The battery in your fone will not suffer with memory issues. This is why you can top up your battery as and when you want.
Check you are shutting down app's when not needed as this causes a massive drain on the battery. So does bluetooth etc.
The n95 battery is well known for being weak.
So if you have done all the above and your still having issues then either your battery is shot or the power management in your handset has issues.
Nokia n8.
iphone 4 16gb - black
Be happy !!