How was this car driving HV Battery problem

2003 Toyota Prius HV battery was swelled on the main cover has exploded cells and was still driving even with the P0A80. The car came in with the dreaded triangle of death and after inspection you could hear a sizzling noise coming from the HV I pulled the main switch pulled the plastic covers and there it was swelled and sizzling needless to say its toast..... will post better pictures when I get back to the garage

 

I have a video how do I post it?

 

A little JB weld some epoxy and duct tape that bad boy would run like a scalded ape

 

I will be able to let you know the cause this evening with pictures as I just picked up another replacement battery from the parts lot

 

Four cells are completely blown fan was full of trash and dog hair....... now the main reason this is the customer's sons car. When it started blowing the dreadful triangle of doom the owners son had it scanned and decided to take matters in his own hands due to low voltage on the HV so he started to crank the car put in drive hold the brake and depress the accelerator charging the HV......... ending result overcharged cells........ do not by any means do this cost to fix $1600

 

Correction and my apologies this is a 2005 prius not a 2003