There's 3 possible issues here apart from software/firmware causes.
1) The USB cable might shorted.
- This can be confirmed by using multimeter to test the usb cable. You will see a shorting between to wire in the USB cable.
2) The Phone USB port might shorted.
- This can be confirmed by using another good/new usb cable and test it with multimeter.
3) Phone battery broken(happened when you charge it using wire and external charger).
- This can be confirmed by trying another Defy battery and charge it.
Defy MB526: Multitouch Custom CM10 - 4.1.2
: Rooted : 2nd-boot : Overclock 1100Ghz: 720P Recorder :
Transformer TF101(B60): JB 4.2.2 (B175)
Custom kernel : Kat Kernel 96 Lidpatch
System Speed: Overclock Dual Core 1400Ghz