Deep sleep mode in a BMS is an ultra-low-power operating state designed to minimise battery drain when the pack is inactive for extended periods. It is particularly important for Li-ion and Li-polymer batteries used in portable, IoT, and standby-powered products.

1. Purpose of Deep Sleep Mode

• Reduce quiescent current to prevent self-discharge

• Extend shelf life and storage time

• Protect cells from over-discharge during inactivity

• Enable compliance with long-term storage and transport requirements

Typical deep sleep current:

• 1–10 µA (basic protection ICs)

• <1 µA for advanced low-power designs

2. Conditions That Trigger Deep Sleep

A BMS may enter deep sleep when one or more of the following occur:

• The shelf life and storage time

• Pack voltage drops to a low-voltage sleep threshold

• The charger is disconnected for a prolonged period

• The host system sends a sleep or shutdown command (smart BMS)

3. Behaviour in Deep Sleep Mode

When active, the BMS will:

• Disable discharge MOSFETs (load disconnected)

• Minimise internal monitoring activity

• Maintain only critical protection functions (OVP/UVP safety)

What stops working temporarily:

• Fuel gauge updates

• Communication (I²C / SMBus / UART)

• Active balancing

• Status LEDs or indicators

4. Wake-Up Conditions

The BMS typically exits deep sleep when:

• A charger is connected

• A voltage is detected on the charge terminals

• A load is briefly applied (design-dependent)

• A wake pin or communication command is asserted

Wake-up time is usually measured in milliseconds to seconds, depending on the design.

5. Deep Sleep vs Normal Sleep vs Protection Shutdown

6. Benefits for Li-Po Battery Packs

• Prevents batteries from reaching over-discharge damage

• Extends storage life from months to years

• Reduces swelling risk caused by deep depletion

• Improves end-user experience after long storage

7. Design and Usage Considerations

• Ensure the wake-up method is compatible with your system

• Some low-cost BMS boards require a charger connection only to wake

• Deep sleep does not replace correct storage voltage practices

• Always verify quiescent current in real hardware, not just datasheets

8. Typical Applications

• IoT sensors and trackers

• Backup battery packs

• Consumer electronics in storage

• Shipping mode for retail products

• Embedded systems with long idle periods

9. lithium-ion battery safety contact

• ACT Emergency Services Agency
• Department of Fire and Emergency Services WA
• Fire and Rescue NSW
• Fire Rescue Victoria
• Northern Territory Fire and Rescue Services
• Queensland Fire and Emergency Services
• South Australian Metropolitan Fire Service
• Tasmania Fire Service

10. Lithium-ion Battery Safety Reports

• CSIRO lithium-ion battery report ( PDF 2.71 MB ) 
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