There are tons on high side switch IC's , but considering the rebound voltage after switch off from a small memory effect due to dielectric absorption, you will want some hysteresis in the control voltage which can be done with a low voltage Schmitt Trigger and voltage divider from Vbat to drive. It can operate from the 1st cell at 3 to 4 V. For longer life Ah try to alert an LED at 50% SOC to remind you to recharge, with another comparator. LEDs can also be used as Zeners, 3V for white, 2V for Red/Yel at 10mA