Formula Used
The calculator first converts load current to battery-side current when a regulator is used.
I_battery = (I_load × V_load) / (V_pack × Efficiency)
The operating mode average is based on active, transmit, and sleep duty cycles.
I_mode = (I_active × D_active) + (I_transmit × D_transmit) + (I_sleep × D_sleep)
Usable capacity includes practical derating factors.
C_usable = C_rated × Parallel × DoD × Health × Temperature × (1 - Reserve)
Self discharge is converted into an equivalent current.
I_self = (C_usable × Monthly self discharge) / 730.5
The final runtime is simple but powerful.
Runtime hours = C_usable / I_total
Battery Life Planning for Electronics
Why Average Current Matters
Battery life is rarely set by one current value. Small devices change state often. A sensor may sleep for minutes. Then it wakes, measures, transmits, and sleeps again. The average current tells the real story. It blends every mode by time. That makes it better than using peak current alone.
Capacity Is Not Fully Usable
A battery rating is tested under controlled conditions. Field use is different. Cold weather can reduce capacity. Old cells can lose strength. Cutoff voltage can leave unused energy. A safe design also keeps a reserve. This calculator applies those factors before runtime is estimated.
Regulators Change the Current
Many circuits run from a regulated rail. The load may use 3.3 volts. The battery may sit near 3.7 volts or higher. A regulator draws battery power to create the output. Efficiency decides the input current. Low efficiency can shorten runtime quickly, especially during transmit events.
Sleep Current Can Dominate
Peak pulses look large, yet standby time may be longer. A few extra microamps can matter over months. Quiescent current also counts. Leakage from protection parts or boards counts too. Long-life products need careful low-power design. Good estimates include every always-on path.
Use Results as a Design Guide
The result is an engineering estimate. It helps compare batteries, firmware duty cycles, and regulator choices. Real tests are still important. Measure current with the final hardware. Test at the expected temperature. Then update the inputs. This loop creates a stronger design and fewer field failures.
FAQs
1. What does this battery life calculator estimate?
It estimates runtime from capacity, average current, duty cycle, regulator efficiency, derating, leakage, and self discharge. It also shows usable capacity, total average current, and an estimated replacement date.
2. Should I use measured current or datasheet current?
Measured current is best. Datasheet values are useful during early design. Final products should be tested with real firmware, sensors, radios, regulators, and expected temperature conditions.
3. What is duty cycle?
Duty cycle is the percentage of time a device spends in a mode. A 5 percent active duty means the device is active for 5 percent of the operating period.
4. Why is regulator efficiency included?
Regulators waste some energy while converting voltage. The calculator converts load-side current into battery-side current when regulated output is selected. Lower efficiency increases battery drain.
5. What is depth of discharge?
Depth of discharge is the share of capacity you plan to use before cutoff. Lower values protect rechargeable cells and provide a more conservative runtime estimate.
6. Why add a reserve margin?
A reserve margin protects against real-world variation. Battery tolerance, temperature, aging, pulse loads, and measurement errors can all reduce available runtime.
7. Does self discharge matter for short runtimes?
It usually matters less for short runtimes. It can matter a lot for products expected to run for months or years, especially with low average load current.
8. Can this replace laboratory battery testing?
No. It is a planning tool. Use it to compare designs and set expectations. Always validate final runtime with real batteries and real operating conditions.