Battery life determines IoT deployment feasibility. Devices requiring battery replacement every 2 years create unsustainable operational costs for large-scale deployments. Understanding how LTE-M, NB-IoT, and legacy 2G compare on power consumption, and what drives the differences, enables accurate battery life projections and informed technology selection.
This guide compares power consumption across cellular IoT technologies, explains power-saving mechanisms, provides real world battery life calculations, and identifies optimisation strategies.
Why Power Consumption Matters for IoT
Operational Cost Impact
Battery Replacement Cost: £10 to 50 per device (battery, labour, logistics)
Scale Impact:
10,000 devices requiring battery replacement every 2 years:
- Replacement cost: 10,000 × £25 = £250,000 per cycle
- 10-year lifecycle: 5 replacement cycles = £1,250,000
If battery lasts 10 years instead of 2:
- Replacement cost: £0 (no replacement needed)
- Savings: £1,250,000
ROI: Investing in low-power technology (LTE-M, NB-IoT) that extends battery 5× pays for itself immediately in reduced operational costs.
Device Design Constraints
Battery Size vs Device Size:
Wearable medical device: Must be lightweight (<50g), comfortable to wear.
Option A: 2G connectivity, 2-year battery life requires 15 Wh battery (heavy, bulky).
Option B: LTE-M connectivity, 10-year battery life achievable with 5 Wh battery (smaller, lighter).
Impact: Low-power connectivity enables smaller, more wearable devices.
Deployment Feasibility
Inaccessible Devices:
Smart metres in basements, sensors in underground infrastructure, trackers on remote assets, physical access expensive or impossible.
Battery replacement is often infeasible, meaning device lifecycle is determined by battery life.
2G (2-year battery): Requires access every 2 years (prohibitive for 100,000 metres).
NB-IoT (15-year battery): Matches metre lifespan (20 years), eliminates replacement need.
Power Consumption Basics
Power States
IoT devices operate in different power states:
Active Transmission:
- Radio transmitting data
- Highest power consumption: 100 to 500 mA
- Duration: Seconds to minutes (depending on data volume)
Active Reception:
- Radio listening for network messages
- Moderate power: 50 to 100 mA
- Duration: Varies (can be always-on or periodic)
Idle (RRC Idle):
- Connected to network but not transmitting
- Radio periodically checks for messages
- Low power: 5 to 20 mA
- Duration: Between transmissions if device doesn’t enter PSM
Sleep (PSM – Power Saving Mode):
- Radio completely off, unreachable from network
- Ultra-low power: 0.001 to 0.01 mA
- Duration: Between transmission cycles (hours to days)
Deep Sleep (Device MCU Off):
- Everything off except RTC (real-time clock)
- Minimal power: <0.001 mA
- Duration: Between wake cycles
Energy Consumption Formula
Energy = Power × Time
Example:
Transmission event:
- Power: 200 mA at 3.7V = 0.74 W
- Duration: 2 seconds
- Energy: 0.74 W × 2 s = 1.48 Wh / 3600 = 0.00041 Wh
Daily transmission (once per day):
- Energy per transmission: 0.00041 Wh
- Daily energy: 0.00041 Wh
- Annual energy: 0.00041 Wh × 365 = 0.15 Wh
Sleep between transmissions:
- Power: 0.005 mA at 3.7V = 0.0000185 W
- Duration: 86,398 seconds (24 hours minus 2 seconds transmission)
- Energy: 0.0000185 W × 86,398 s = 1.6 Wh / 3600 = 0.00044 Wh per day
- Annual sleep energy: 0.00044 Wh × 365 = 0.16 Wh
Total annual energy: 0.15 Wh (transmission) + 0.16 Wh (sleep) = 0.31 Wh
Battery life with 5 Wh battery: 5 Wh / 0.31 Wh/year = 16.1 years
Technology Comparison: LTE-M vs NB-IoT vs 2G
Transmission Power
Active Transmission Current:
2G (GPRS/EDGE):
- Peak current: 250 to 400 mA (class 4: 2W, class 5: 0.8W)
- Average during burst: 180 to 300 mA
LTE-M (Cat-M1):
- Peak current: 200 to 350 mA (power class 3: 23 dBm)
- Average during transmission: 150 to 250 mA
NB-IoT (Cat-NB1/NB2):
- Peak current: 150 to 300 mA (power class 3: 23 dBm)
- Average during transmission: 120 to 220 mA
Observation: All three similar during active transmission, differences emerge in idle and sleep states.
Idle Power Consumption
Between Transmissions (RRC Idle, not PSM):
2G:
- Idle current: 2 to 10 mA (varies by implementation)
- Paging reception every 2.12 seconds
LTE-M:
- Idle current: 1 to 5 mA
- Paging reception (if eDRX not configured): 1.28 seconds
NB-IoT:
- Idle current: 0.5 to 3 mA (lower due to simpler receiver)
- Paging reception (if eDRX not configured): 1.28 seconds
Impact: If device doesn’t enter PSM (remains idle between transmissions), 2G consumes most power.
Sleep Power Consumption (PSM)
Power Saving Mode (deep sleep, radio off):
2G:
- PSM not standardised (limited support)
- Typical idle: 2 to 10 mA (cannot fully sleep whilst maintaining registration)
LTE-M:
- PSM standardised (3GPP Release 13)
- PSM current: 0.005 to 0.015 mA
- Wake time: 10 to 30 seconds (re-register on network)
NB-IoT:
- PSM standardised (3GPP Release 13)
- PSM current: 0.003 to 0.010 mA (slightly lower than LTE-M)
- Wake time: 15 to 60 seconds (longer re-registration vs LTE-M)
Impact: LTE-M and NB-IoT support deep sleep (PSM), reducing idle power by 1,000×. 2G cannot achieve equivalent sleep states.
eDRX (Extended Discontinuous Reception)
Between PSM and Always-Idle:
2G:
- eDRX not supported
- Device must remain in idle (2 to 10 mA) to be reachable
LTE-M:
- eDRX supported (3GPP Release 13)
- Sleep intervals: 20.48 s to 2,621 s (~44 minutes)
- Average current (eDRX): 0.1 to 0.5 mA (depends on wake interval)
NB-IoT:
- eDRX supported (3GPP Release 13)
- Sleep intervals: 20.48 s to 10,485 s (~3 hours)
- Average current (eDRX): 0.05 to 0.3 mA (slightly lower due to longer intervals possible)
Impact: LTE-M and NB-IoT enable configurable sleep/wake cycles, device sleeps most of the time, wakes periodically to check for messages. 2G must remain always-idle (higher power).
Real-World Battery Life Calculations
Assumptions
Battery: 5 Wh (common for AA or C-cell lithium)
Operating voltage: 3.7V
Transmission: Once per day, 200 bytes payload, 2 seconds duration
Signal strength: Good (-80 dBm)
Temperature: 25°C (affects battery capacity)
Scenario 1: Daily Transmission, PSM Between
2G (No PSM):
Transmission (once/day):
- Current: 250 mA, duration: 2 s
- Energy per transmission: (250 mA × 3.7V × 2s) / 3600 = 0.00051 Wh
- Daily transmission energy: 0.00051 Wh
Idle between transmissions (24 hours minus 2 seconds):
- Current: 5 mA, duration: 86,398 s
- Energy: (5 mA × 3.7V × 86,398s) / 3600 = 0.445 Wh
- Daily idle energy: 0.445 Wh
Total daily energy: 0.00051 + 0.445 = 0.445 Wh
Battery life: 5 Wh / 0.445 Wh/day = 11.2 days
Annual replacements: 365 / 11.2 = 32 batteries per year (infeasible)
LTE-M (PSM):
Transmission: Same as 2G = 0.00051 Wh/day
PSM sleep:
- Current: 0.01 mA, duration: 86,398 s
- Energy: (0.01 mA × 3.7V × 86,398s) / 3600 = 0.00089 Wh
Total daily energy: 0.00051 + 0.00089 = 0.0014 Wh
Battery life: 5 Wh / 0.0014 Wh/day = 3,571 days = 9.8 years
NB-IoT (PSM):
Transmission: Current 200 mA (lower than 2G) = 0.00041 Wh/day
PSM sleep:
- Current: 0.006 mA, duration: 86,398 s
- Energy: (0.006 mA × 3.7V × 86,398s) / 3600 = 0.00053 Wh
Total daily energy: 0.00041 + 0.00053 = 0.00094 Wh
Battery life: 5 Wh / 0.00094 Wh/day = 5,319 days = 14.6 years
Comparison (Daily Transmission, PSM):
- 2G: 11 days
- LTE-M: 9.8 years (320× longer)
- NB-IoT: 14.6 years (476× longer)
PSM is game-changer.
Scenario 2: Hourly Transmission, PSM Between
LTE-M (PSM):
Transmission (24 times/day):
- Energy per transmission: 0.00051 Wh
- Daily transmission energy: 0.00051 Wh × 24 = 0.012 Wh
PSM sleep (23 hours, 59 minutes, 12 seconds total):
- Same as scenario 1: 0.00089 Wh
Total daily energy: 0.012 + 0.00089 = 0.013 Wh
Battery life: 5 Wh / 0.013 Wh/day = 385 days = 1.05 years
NB-IoT (PSM):
Transmission: 0.00041 Wh × 24 = 0.010 Wh
PSM sleep: 0.00053 Wh
Total daily energy: 0.010 + 0.00053 = 0.011 Wh
Battery life: 5 Wh / 0.011 Wh/day = 455 days = 1.25 years
Comparison (Hourly Transmission):
- LTE-M: 1.05 years
- NB-IoT: 1.25 years
More frequent transmission significantly reduces battery life, even with PSM.
Scenario 3: Daily Transmission, eDRX (Not PSM)
Use case: Device needs to receive messages from backend (firmware updates, configuration changes) but not always connected.
LTE-M (eDRX, 10-minute wake intervals):
Transmission: 0.00051 Wh/day
eDRX sleep (wake every 10 minutes):
- Average current during eDRX cycle: 0.3 mA
- Energy: (0.3 mA × 3.7V × 86,398s) / 3600 = 0.027 Wh
Total daily energy: 0.00051 + 0.027 = 0.027 Wh
Battery life: 5 Wh / 0.027 Wh/day = 185 days = 6.1 months
NB-IoT (eDRX, 60-minute wake intervals):
Transmission: 0.00041 Wh/day
eDRX sleep:
- Average current: 0.1 mA (longer intervals = less frequent wake)
- Energy: (0.1 mA × 3.7V × 86,398s) / 3600 = 0.009 Wh
Total daily energy: 0.00041 + 0.009 = 0.009 Wh
Battery life: 5 Wh / 0.009 Wh/day = 556 days = 1.5 years
Comparison (eDRX):
- LTE-M (10-min wake): 6.1 months
- NB-IoT (60-min wake): 1.5 years
eDRX significantly reduces battery life vs PSM. Use PSM when possible.
Factors Affecting Real-World Battery Life
Signal Strength
Poor Signal = Higher Power:
Device in area with weak signal (-110 dBm vs -80 dBm):
- Must transmit at higher power to reach tower
- Takes longer to establish connection (more retransmissions)
- Both increase energy consumption
Impact:
Good signal (-80 dBm): 10-year battery life
Poor signal (-110 dBm): 3-year battery life (70% reduction)
Mitigation:
- Validate coverage before deployment
- Use external antenna in marginal signal areas
- Choose NB-IoT (better coverage) for challenging environments
Temperature
Cold Reduces Battery Capacity:
Lithium battery capacity decreases in cold:
- 25°C: 100% capacity
- 0°C: 85% capacity
- -20°C: 60 to 70% capacity
Impact:
Device rated 10-year battery life at 25°C:
- At 0°C: 8.5 years
- At -20°C: 6 to 7 years
Mitigation:
- Use cold-rated batteries (lithium thionyl chloride for -40°C to 85°C)
- Oversize battery for cold environments (7 Wh instead of 5 Wh)
- Account for temperature in battery life calculations
Data Volume
More Data = More Power:
Transmission duration proportional to data volume:
- 100 bytes: 1 second transmission
- 1 KB: 5 seconds
- 10 KB: 20 seconds (NB-IoT), 8 seconds (LTE-M)
Impact:
Daily transmission, 100 bytes vs 10 KB:
- 100 bytes: 10-year battery
- 10 KB: 5-year battery (50% reduction)
Mitigation:
- Compress data before transmission
- Send deltas (changes only), not full state
- Batch readings (send 24 hours of data once vs hourly reports)
Transmission Frequency
Frequency Dominates Battery Life:
Device transmitting once per day vs once per hour:
- Daily: 10 years
- Hourly: 1 year (90% reduction)
Transmission frequency has larger impact than data volume.
Mitigation:
- Transmit only when necessary (threshold-based, not time-based)
- Batch data (buffer locally, transmit in bulk)
- Adaptive frequency (transmit hourly during events, daily during steady state)
Network Registration Overhead
Wake from PSM = Network Re-Registration:
Each wake from PSM:
- Device re-registers on network (attach procedure)
- Duration: 10 to 60 seconds
- Power: 50 to 200 mA
Frequent PSM wake/sleep cycles waste energy on registration.
Example:
Wake every 10 minutes (144 times/day):
- Registration energy: 144 × 0.0005 Wh = 0.072 Wh/day
- Battery life: 5 Wh / (0.072 + transmission) ≈ 2 years
Wake once per day:
- Registration energy: 0.0005 Wh/day
- Battery life: 10 years
Mitigation:
- Minimise PSM wake frequency
- Use eDRX if frequent wakeability needed (avoids re-registration)
- Batch transmissions (don’t wake separately for each sensor reading)
Optimising Battery Life
- Choose Right Technology for Use Case
LTE-M:
- 10 to 15 year battery achievable with daily transmission
- Best for moderate data, mobility, low latency needs
NB-IoT:
- 15 to 20 year battery achievable with daily transmission
- Best for ultra-low power, stationary, infrequent transmission
Don’t use 2G for new deployments, inferior power consumption and sunset imminent.
- Maximise PSM Usage
Configure PSM with longest acceptable sleep interval.
Example:
Use case: Smart metre reading once per day at 3am.
PSM timer: 86,400 seconds (24 hours)
Device:
- Wakes at 3am
- Transmits reading
- Returns to PSM immediately
- Sleeps until next 3am
Battery life: 15+ years
Don’t: Stay in idle/eDRX when PSM sufficient.
- Minimise eDRX Wake Frequency
If eDRX necessary (device must receive messages), configure longest acceptable interval.
Example:
Firmware updates sent monthly (not daily).
eDRX wake interval: 3 hours (not 10 minutes)
Impact:
10-minute eDRX: 6-month battery
3-hour eDRX: 3-year battery (6× improvement)
- Compress and Batch Data
Transmit efficiently:
Inefficient:
- 10 sensor readings/day
- Transmit each reading individually (10 transmissions/day)
- Battery life: 2 years
Efficient:
- 10 sensor readings/day
- Buffer locally, transmit batch once/day (1 transmission/day)
- Compressed payload
- Battery life: 10 years (5× improvement)
- Adaptive Transmission
Transmit frequently only when necessary.
Example: Tank Level Monitor
Fixed schedule: Report level every hour (24 transmissions/day)
Adaptive:
- Level stable: Report once per day
- Level changing: Report every hour
- Level critical: Report every 10 minutes
Result: Average 2 transmissions/day (vs 24), 10× battery life extension.
- Validate Coverage and Optimise Antenna
Poor signal = wasted power.
Before deployment:
- Test signal strength at actual locations
- If signal marginal (-100 to -110 dBm), install external antenna
- External antenna improves signal 5 to 10 dB = 2 to 3× battery life extension
Cost: £5 antenna vs £25 battery replacement every 3 years (instead of 10).
Technology Selection Based on Battery Requirements
20-Year Battery Life Required
Use Case: Smart metres, sealed industrial sensors, inaccessible devices
Technology: NB-IoT with PSM
Configuration:
- Transmission: Daily or less frequent
- PSM between transmissions
- Data volume: <1 KB per transmission
- Good signal coverage
Achievable: 20+ years with 5 to 7 Wh battery
10-Year Battery Life Required
Use Case: Asset trackers, wearable devices, outdoor sensors
Technology: LTE-M or NB-IoT with PSM
Configuration:
- Transmission: Daily to hourly
- PSM between transmissions
- Data volume: 1 to 10 KB per transmission
Achievable: 10 to 15 years with 5 Wh battery
2 to 5 Year Battery Life Acceptable
Use Case: Applications with regular maintenance windows, replaceable batteries
Technology: LTE-M with eDRX or limited PSM
Configuration:
- Transmission: Hourly to every few minutes
- eDRX or short PSM intervals
- Moderate data volume
Achievable: 2 to 5 years with 5 Wh battery
<2 Year Battery or Mains-Powered
Use Case: High-frequency data, real-time applications, vehicle-powered devices
Technology: LTE Cat-1 or standard LTE
Configuration:
- Always-connected or very frequent transmission
- No PSM (responsiveness required)
- High data volume
Battery: <2 years or mains/vehicle power required
OV Low-Power Connectivity
LTE-M and NB-IoT: Support for both technologies. Choose optimal for your use case.
PSM/eDRX Configuration: Platform allows custom PSM timers and eDRX intervals per device or fleet.
Coverage Validation: Trial SIMs for real-world signal testing, optimise battery life via coverage validation.
Battery Life Estimation: Tools to calculate expected battery life based on your transmission patterns, data volumes, PSM configuration.
Contact OV to discuss low-power IoT connectivity: connectivity@worldov.com
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