Weight of the actual battery is not the issue, % of lithium makes the difference
In thermal runaway event the ratio surface/volume is important. Little batteries (laptops, phones etc.) have big ratio surface/volume so they are better cooled and the thermal runaway is not so probable.
MH370 may never be found, even MS804 may not be found
A few hundred miles away, near Beirut, the wreckage of MH240 is lying on a seabed. Not deep and completely with FDR and CVR on board. Nobody wants to lift it...