battery power storage
A custom battery pack should have thermal protection to prevent cell damage or rupture during charging or discharging. The standard is to use an NTC thermistor 10K/25. That is, R25°C=10KΩ, and B=3950. B is the sensitivity index constant. Note that 25°C=298.15°K. To calculate temperature from resistance, T = B / (ln(R/r∞)).
An NTC thermistor can also be used for surge protection. It gives a soft start when equipment is first powered up. When powering up the NTC is cold and resistance is high thus limiting current. As the current floww the NTC thermistor will get warmer. This causes resistance to drop which removes the current limiting factor from the circuit.