5100 battery for NOKIA mobile phone

How to Unlock Nokia Cell Phone
1, Before trying anything else, contact your service provider and ask for an unlock code. Usually, if you've been a customer of theirs for some time, they will provide you with an unlock code for free. This is, by far, the best way to get your phone unlocked.
2, Download software to generate the unlocking code. Software is available on some websites for free and some pay websites that also offer support if things go wrong. See external links below.
3, Find the Serial number of the cell phone, also known as your IMEI number. This can be done by either removing the back of your cell phone and looking underneath the battery, or simply by typing in *#06# into your cell phone. It should be something like: 010082321439976/07951780736
4, Using the software you have downloaded, enter in your Manufacturer (which is in this case Nokia), and sliding the card out. Put the battery back in and power the phone on.
5, You will see a message "Insert SIM Card". Enter all of the characters you see in your code, including the # symbols. To get a 'p' press * 3 times, to get a '+' press the * key 2 times, to get a 'w' press the * key 4 times. Disregard any spaces in the code.
6, In order to unlock your phone you generally need to enter only one code. Start with the first one. If your phone is not unlocked by typing the first code (MCC+MNC), use code "7" (Multilock)
7, Once you have finished entering a code that works you should see a message that says "SIM is not restricted" or "Restriction off" message depending on your model. If not, try entering another code. Message "Cannot undo restrictions" means the phone is "hard-locked" and cannot be unlocked by code.

NOKIA 5100 Mobile Phone Battery Descirption
Battery Chemistry: Li-ion
Battery Voltage: 3.70V
Capacity: 700mAh
Color: Black
Dimension: 53.30 x 34.05 x 4.60 mm
Weight: 17.01 g
Compatible Battery Code:BL-4C
Fits Models: 1265, 1325, 1508i, 2650, 2651, 2652, 2865, 3108, 3500 classic, 5100, 6006, 6008, 6066, 6100, 6101, 6102, 6102i, 6103, 6125 , 6126, 6131, 6133, 6136, 6170, 6260, 6300, 6300i, 6301, 7200, 7270, 6260 fold, 1661, 1202
Unlocking applies to all cellular phones. The steps provided above work for GSM phones. You CANNOT use the steps above to unlock a CDMA or TDMA phone. To "unlock" a CDMA or TDMA phones is known as reprogramming the phone. For CDMA phones, you need the Master Subsidary Lock or MSL, which you MAY be able to get from your service provider. Please note that you may not be able to get the MSL from your service provider, as it usually is against company policy to give these to customers.

Warnings
Attempting to unlock your phone is done at your own risk. Although unlocking your phone is legal, some cell phone operators might choose to void your warranty should you unlock your phone (then again, some cell phone operators won't mind).
Most phones only allow you to try a certain number of unlock tries, Nokia phones have a limit of 5 tries. After that, the phone becomes "hard-locked", meaning it cannot be unlocked without using special equipment.
Most of the newer phones will not work with the codes generated by the free unlock programs.