Rechargeable Battery for Lego Mindstorm NXT Any Version

WARNING: polarity must be check 3 times to make sure before connecting battery think of this as one shot deal. These will effect warranty on product so if u got warranty don't try it PLZ. If you really want to do it go a head to next step.

Step 1: Materials

   The material u will need are:
1.  Any rechargeable battery pack you have or you can get
NI-MH adn NI-CD batery are acceptable 
make sure they are 7.2 volts NOT over
i recommend NI-MH battery
give better run time
2. connection 
RC 7.2V Battery Pack Connector Repair Kit
you can get it at radioshack or any broken charger or Toy 
3. Last thing is the NXT robot

Step 2: Solder Connections or the Way You Want to Do It.

Connections: solder the connections to the battery holder on NXT as shown in the picture
before you solder them make a nod then solder them into place.

Step 3:

Make double or triple check that the connections are in the right polarity before connecting the battery. these will save you $50 on battery from lego and it might even save you shipping. 
In total these should be $25 or nothing if you already have the battery and the other stuff.

video
http://www.youtube.com/watch?v=29Rn4AEwP_s