Our IoT battery packs are formed by combining low current lithium thionyl chloride LiSOCl2 cells (ER cells) and low internal resistance rechargeable lithium cells (HPCs or Hybrid Pulse Capacitors). The HPCs store sufficient energy to supply the high current pulses and the ER cells slowly recharge the HPCs between the pulses. HPCs have much lower internal resistance than the ER cells and thus can supply the high current for the application. By recharging the HPCs slowly, the ER cells lose less energy to internal resistive losses. This improves the pack’s overall efficiency and allows it to produce more useful energy from the pack’s ER cells.