The A320 has the older Nicad batteries. Airbus has recently stated that they will start to install Lithium batteries in the A350. Just to note after Boeing redesigned the 787 batteries there has been only 1 venting event with no fire.
You miss understand me. I am not assuming anything. In fact, my personal opinion is that it wasn't terrorism but some kind of electrical fire. My point is that there was a fire onboard doesn't mean it was mechanical or electrical. It could be something in the cargo. It could be some idiot smoking in the lav. It could be a major electrical problem. Or, it could be someone planting a fire bomb onboard --- http://www.dailymail.co.uk/travel/travel_news/article-3178623/Chilling-footage-shows-panic-cabin-Chinese-airliner-passenger-tries-start-fire-petrol-smuggled-board.html