My BC-9009 overheated yesterday upon the first use. I used the Lacrosse branded 4 AA 2600 maH batteries supplied. In the test mode, the 4 batteries each topped off to full charge using the 1000ma charge rate in approx. 10 minutes at which point the charger switched to discharge at the 500ma rate. In about 5 hours the first battery reached the 100% discharge threshold (0.90v) and this channel switched back to charge although it showed only 250ma rate and this was quite variable. Within several minutes I felt a hot spot through the bottom at this battery position. Within 10 minutes and before the other batteries could reach their respective discharge terminations, the button at this first battery position had melted down and sunk.
Interestingly, the charger still retains full function. Perhaps if I hadn't intervened so quickly the failure may have been more progressive. So this isn't a irreversable failure of a component - but something physically incorrect in this particular charger by design or build.
I repeated the test cycle above. Again, the same channel  reached the discharge threshold and the charger switched into charge mode, charging at indicated apprx 250ma. The electronics at that position reacted and overheated in the same manner. After about 10 minutes the LCD began to flash between "full" and the subnormal charge current. Then position 1 switched over to charge. The channel 1 button proceeded to meltdown in the same manner and that channel reached the same end point after about 10 minutes. Then positions 3 & 4 switched to charge but, after a brief time at 250ma, these went to the proper 1000ma charge current. Channels 1 & 2 after the thermal event appear to shut down or stabilize.
Even with buttons 1 and 2 melted down the charger still functions. I next decided to try the test cycle again, selecting down to the 700ma charge rate. All 4 channels successfully made the complete round trip. So, with no big surprise, my thermal problem appears to be related to the 1000ma charge rate, and maybe using a completely discharged battery.