Yup, there are other reasons that can cause the battery to fail and swell, but the heat issue is a big one and affects all chemistry - some more than others - but a higher environmental temp when charging and discharging under load will cause more failures than a lower temperature. So the slim laptops that can't / don't vent heat will cook the batteries with a larger percentage of swollen failures than a large laptop with adequate cooling. The thin and light laptops just don't have the volume to hold enough mass to sink the heat and large enough heat exchangers or fans to expel the heat. The large frame laptops have the physical characteristics that allow them to pack in cooling hardware enough to vent out the heat constantly enough to keep the laptop from heat soaking - holding in the heat until it builds up to dangerous levels for the battery. You can also get bad battery design and chemistry which we've seen in laptops and phones. But the heat issue is what causes the failures even with good battery design and chemistry - IDK if they can come up with a design / chemistry to stop swollen batteries that are heat soaked. They could design the battery with active cooling? - but there again more room would be needed for the battery active cooling and there is no such room in a thin and light laptop. It makes sense to buy a large frame laptop if performance is your goal - gaming in AAA games for one - as the small thin laptops can't handle continuous load without continuously building up heat.