File:Battery-powered preamp - power management (UVLO, muting delay).png

English: A simple power management circuit for a battery-powered phono stage. The PMOS and the first relay do the ON-OFF and undervoltage lockout (UVLO); the second relay is for the muting delay (5s in this example). 6S1P lithium stack connected via a 6S BMS board. Relays are rated for 12V, well, simply because I had hundreds of these already; otherwise an RY24-K would be a better proposition. Both relays are driven via RC networks, so they get the full rated voltage at turn-on, but only around 2..3V afterwards. Thus, the continuous DC through each relay is around 2...3mA. The datasheet says that this relay has a release voltage of 0.6V, but in practice it shouldn't drop below 1.5V or so.
The purpose of R23 is to effectively short the power supply terminals of the preamp in off-state, discharging the preamp's own power filter capacitors. At the same time, R23 provides a fast, low-impedance discharge path for the capacitors C31, C32 - to reset the muting relay. Likewise, shorting R13 to ground (manually) discharges C11, C21. R13, R23 must be rated at least 1W to handle the transients.
The purpose of C11 is to ensure that the PMOS is OFF immediately after connecting the battery. Without C11, the power-up transient may force the latch into ON state. C11 isn't really required because the user can reset the latch manually after replacing the batteries.
The purpose of many diodes is to speed up discharge of the capacitors at turn-off or at power-down. They are not critical for safety; the small relay used here cannot create truly destructive inductive spikes.
BMS boards have UVLO functionality, so adding another UVLO stage might seem unnecessary. My reasoning was that (a) the quality and the UVLO setting of a particular board may be substandard (b) it makes sense to set the UVLO higher than the minimal stock value and (c) it costs pennies, who cares.