If you aren’t going to use a BMS to protect the cells on your battery pack then you need to use a cell checker. It will measure the voltage of each cell group as well as the overall pack voltage AND it will sound an alarm if the voltage drops below a pre-set level (you can choose the minimum voltage to sound the alarm).
Any responsible lithium battery builder that doesn’t use a BMS should have a cell checker and cell alarm. Some even add a balance connector to packs with a BMS to use one of these for additional peace of mind and to perform spot checks on cell packs inside the battery pack.
Simply plug the cell checker into the balance connector on your pack and watch as it cycles through all of the cell groups, listing each group’s voltage.
To set the low voltage alarm voltage, simply press the button at the top of the device after plugging the device into your battery’s balance connector. Each time you press the button, the screen will increase the voltage level by 0.1 V. We recommend setting the low voltage warning at 3.0 V to ensure that it gives an early warning before the common 2.7 V minimum cutoff.
Don’t forget to unplug it from your battery when you aren’t using it though, as the screen displaying the voltage will stay on and slowly consume your battery over a period of days and weeks.