First, what is thermal runaway? A battery is considered to be experiencing a thermal even when the battery begins to generate heat from uncontrolled self-discharge. Essentially, the battery is generating more heat than there is the possibility for it to transfer the heat into its environment. Sealed Lead Acid (SLA) batteries. The usual cause of uncontrolled high-rate self-discharge is an internal short. An internal short most often occurs when a battery is misused. Dropping a battery, over charging and over. An internal short is when two of the lead plates are very near, or even touching each other, often due to a failure of the separator material. Having. Internal shorts can be best avoided through careful SLA battery construction. Power Sonic goes to great lengths of putting in the effort required to ensure high manufacturing quality. These high standards are in place to. While enough heat is generated to boil the acid, this temperature is far below any flash point that may cause fire. The temperatures are.