Cordless Drill battery rebuilt again

Once again I have become totally frustrated with my cordless drill. The batteries do not last very long and do not have enough power.  So this time I bought 4 of these 1800ma 4.8 volt battery packs and connected them together to make a much more powerful battery pack.

Now in order to get 18 volts I had to remove one of the batteries from one of the battery packs.  This new battery pack is about 1/4 the weight of the old battery pack.  The last time I did this I used individual AA rechargable batteries and when a 1 inch paddle bit got stuck in a wall the wires in the battery pack melted.  So this time I used much bigger wires to connect up the batteries hoping it will hold up better.

This is what it looks like untill I put the top cover back on.  Note the temperature sensor sticking out the left side, that needs to be taped or glued onto one of the batteries.