The pacemaker is powered by a battery with the lifetime of about 8 decades, for the normally used lithium batteries, to many dozen several years to the nuclear batteries. Since the pacemaker is actually a disposable and implantable gadget, the preserving of battery energy is vital for that lifetime extension. https://tedomarket.com/product/computers-and-network/power-bank/battery-capacity/10001-15000mah/vinsic-alien-p7-ultra-slim-15000mah-power-bank-portable-external-battery-charger-dual-usb-for-iphone-x-8-8-plus-samsung-s8-s8-2/