UVLO with a battery can be tricky since the battery voltage will go back
up again when the load is removed. Some regulators (both linear and
switchers) have UVLO built in. If you can afford the current draw, an
electromechanical relay can provide UVLO with hysteresis. MANY years ago,
I made a latching relay circuit with a standard resistor and two
resistors. There was a resistor from one end of the coil to ground. A
resistor from the other end went to the DC supply. The resistors were
chosen such that the current through the coil was half way between the
pull-in and drop-out currents. A contact closure from the "bottom" of the
coil increased the current to above the pull-in current. The relay pulled
in. Removing the contact closure dropped the current back to the middle
current, which was sufficient to hold the relay closed. A contact closure
from the "top" of the coil to ground caused no current to go through the
coil, so the relay dropped out. Removing the contact closure returned the
coil current to the mid value. High enough to hold, but not enough to pull
in. Since the relay was released, it stayed released.

Anyway, I've used relays for UVLO on lead acid batteries.

Harold


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