Lenovo ThinkPad Edge E320?
I don't think you are referring to the Main battery......
1) There is a slide button on each side of the Main battery.
Both are slid to the outside edges of the laptop, then the main battery is slid out. Out towards the outside of the laptop.
I believe you are referring to the CMOS battery.
Also known as the RTC battery. Real Time Clock battery.
From what I can see the ThinkPad Edge E330 is VERY similar to the ThinkPad Edge E320.
What you need is the HMM. Hardware Maintenance Manual,http://www.manualowl.com/m/Lenovo/ThinkPad-Edge-E330/Manual/309892
Use the Right Arrow on the right side of the number 100, at the top; to go down through the pages.
Page 61 for Main Battery Removal/Replacement
(Starts on Page 60 - 1010 Battery Pack. Bottom of page)
Page 70 for RTC Battery Removal/Replacement
Bottom of the page - 1070 Backup Battery
As you can see you just remove the screws, (Philips. Use No.1 Philips screwdriver, or equivalent Jewelers screwdriver), for the Bottom Cover, and remove the Bottom Cover.
(It's a panel. It is not the Base Enclosure/Bottom Cover)
Then unplug the small white male plug connector, on the end of the RTC Battery's wires; from the motherboard.
Remove the RTC Battery, and replace.
This shows you in a video, but a different Lenovo ThinkPad Edge laptop.
Principle is still the same,http://support.lenovo.com/en_US/downloads/detail.page?DocID=PD021754
KNOW THIS HOWEVER........
Your body carries Static electricity. When that Bottom Cover is removed, all of the Static shock sensitive hardware components are exposed.......
You need to make SURE your body is relieved of Static, BEFORE reaching to unplug that RTC battery, or remove it.
Better still is to wear an ESD wrist strap, and have it's alligator clip attached to a good ground source.
(Electro Static Discharge)
Average cost is around $3 to $6.
Here is but one example,http://www.radioshack.com/product/index.jsp?productId=2103245
Example of RTC Battery,http://www.ebay.com/itm/COMPATIBLE-Backup-RTC-CMOS-BIOS-BATTERY-CR2032-FOR-IBM-Thinkpad-02k6541-/251250253852?pt=Laptop_Batteries&hash=item3a7faea01c
Now I did NOT state that this was THE RTC Battery you need.
Just stating that is what it looks like.
ALL of these batteries produce 3 Volts DC.
They use a CR2032 watch type battery, that is commonly used in a desktop computer.
All you need to make sure of, is the Male Plug Connector is correct.
Yep. That's it.........
If you HAVE to, you could cut the wires on the new RTC Battery, cut the wires on the old RTC Battery, and PROPERLY splice the old RTC battery's male plug connector to the new one.
Use heat shrink tubing, and solder the wires together.
Remove RTC Battery to reset a password?
Nope. Don't think so.
There should be a capacitor, or capacitors; that store a small residual charge of power -> INDEFINITELY, even after removing the RTC Battery. (CMOS battery)
CAN I be wrong? Yep. Depends on manufacturer, and year made.
Replace RTC Battery because it's no good?
Looking at the Base Enclosure, (Bottom Cover), is part of what makes me think the E330 is very close to the E320,http://www.pcworld.idg.com.au/review/notebooks/lenovo/thinkpad_edge_e320_129834m/397569/images?image=5http://support.lenovo.com/en_AU/product-and-parts/detail.page?DocID=PD024121
For additional questions please post in a Comment.