The fuse blown and i had the red/yellow lights of death, i opened it up and found that the fuse had a poor connection to the board via a push fit type connection, the heat produced by this made the thermal fuse blow. I removed the fuse and soldered the heater supply cables directly to the PCB, at the time it was just to see if i could fix it and get it working with a view to replace the fuse later.
http://fuckcombustion.com/threads/the-crafty-by-storz-bickel.15984/page-212#post-814003
I've done 3 swaps, although i could have gone much longer between swaps I just like the fast heat up time and snappy performance with a newer cell. I am only using cheap Samsung 25R's 2500mAh and 20A rated i think, i brought a load about 18 months ago for some other gadgets i was upgrading. The performance does drop just like the original and any other battery, but i doubt it would last as many cycles as the original 2700 Panasonic. Its still much faster heating up than the original due to its lower internal resistance, and the extra impedance removed from the thermal fuse. The trade off is it gets a bit warmer and it has less overall capacity. Although that does not bother me as its always charged after every session and left ready to be picked up again, unless i take it out with me. If I remember correctly when a cell was first installed it heat up in 1.20seconds/190C which is nice, although the time increases to about 1.50 after the first 25/30 hours on a new 25R cell, then very slowly increases. Because I still have a few of these cells i will just change them out when i feel its taking a bit longer than I like to heat up.
I did not replace the fuse, i did order some replacement fuses but because i was loving the performance with the heater cables soldered directly to the board i never replaced it. If you are buying a battery specifically for the crafty i would not use the 25R. I'm sure somebody else will be able to guide you to a better battery to suit the needs required. You ideally want the best performing battery at the time of purchase, new cells are being brought out regularly. Capacity is not as important, discharge and voltage holding under discharge are more important, along with cycle life and temperature under discharge.
the thermal fuse is sw-127T 184C
http://www.conrad.com/ce/en/product/419006/Thermal-fuse-184-C-10-A-250-V-ESKA-SW-127T-1-pcs