Whitepaper
1 How to Select the Right Battery for BLE Asset Trackers and Temperature Loggers
Zinergy is frequently asked “Which battery is best for BLE asset trackers and temperature loggers?”
Usually our customers know:
- How long the device must operate
- How often it should transmit (advertise) data
- The required shelf life before activation
- The BLE chipset they will use.
With this information, knowing the energy used by the chipset for each BLE advertisement and during sleep mode, we can calculate the theoretical battery capacity required.
But it is important to ask whether, provided the battery specification meets the minimum input voltage required by the BLE chipset, is capacity the only parameter to consider?
In practice there are subtleties in battery selection that directly affect product performance, lifetime, and cost. In this article, we explain why choosing the right battery is about more than just capacity.
2 Voltage: More Than a Number
The first consideration is the minimum input voltage your BLE chipset can tolerate without resetting, or “browning-out”. The battery must remain above this voltage for the device’s entire operating lifetime to maintain data integrity and traceability.
While buck-boost converters and power management circuits can extend usable voltage range, they add cost, size, and complexity. For low-cost, high-volume devices, the most economical solution is usually to select a battery that is designed to stay above the minimum input voltage throughout the device’s operating life.
There is a common misconception that: “If my BLE chipset works down to 1.4 V, then a 1.5 V battery should be fine, shouldn’t it?”
Unfortunately, this is rarely true.
Battery voltage is specified at full charge. As the battery discharges, its output voltage gradually declines. So even a “3 V” or “1.5 V” battery will spend a portion of its life below its nominal voltage. Your design must account for the battery’s entire discharge curve—not just the starting point.
3 Internal Resistance: The Hidden Limiter
Every battery has internal resistance (Rint). When current (I) is drawn, the battery’s instantaneous output voltage drops according to Ohm’s Law:
Vdrop = I x Rint
BLE transmissions demand short but significant current pulses. If the battery has high internal resistance, these pulses cause a voltage drop – sometimes enough to trigger a reset or brown-out, even when the battery still has plenty of capacity remaining.
For example:
- Zinergy’s thin, flexible batteries typically have an internal resistance of between 3 and 10 Ω. A 15 mA pulse current may cause the voltage to drop by 0.15 V.
- Alternative manufacturers printed batteries have internal resistances of 50 – 90 Ω.
For the same 15 mA pulse, the voltage drop can approach 0.75 – 1.35 V.
This is why a 1.5 V battery is generally unsuitable for a BLE chipset with a 1.4 V minimum input voltage: The instantaneous voltage drop during transmission leaves no margin, especially if the battery is already partially discharged, and the chip will brown out.
Key point:
Internal resistance can be just as important as nominal voltage and capacity in determining usable lifetime.
4 Aging Effects
All dry batteries age, whether in use or sitting on the shelf. Two things happen during ageing:
- Nominal voltage decreases
- Internal resistance increases
This combination accelerates the point at which the battery can no longer support the pulse currents required by BLE transmissions. Starting with the correct voltage and a low internal resistance is therefore critical to achieving long operational life.
Zinergy’s batteries are designed with class-leading low internal resistance, helping ensure stable performance over time.
5 Operating Temperature
Ion mobility, which is the ability of charged ions to move through the battery, is reduced as temperature falls, causing internal resistance to increase and output voltage to drop as current is drawn. Unless this is considered, it can lead to earlier than expected brown-out.
Consequently, if you aim to use a battery consistently at temperatures below freezing, it is important to understand the battery’s temperature-related properties and compensate by either using a higher voltage, or a battery with a larger capacity. Both approaches can mitigate low temperature effects.
Zinergy undertakes extensive battery testing using in-house programmable battery testers and environmental chambers, characterising our batteries across the full range of operating temperatures.
Zinergy batteries are designed to operate at temperatures as low as -30°C (-22°F).
6 Pulse Loads and Recovery
Battery capacity specifications are traditionally based on continuous, steady current discharge. Asset tracking devices, however, draw current in short bursts while communicating, with relatively long sleep periods in between.
Zinergy batteries are well suited to this usage pattern. They exhibit strong voltage recovery during relaxation periods between transmissions. The longer the rest period, the more the voltage recovers. In practice, this means:
- More stable voltage during advertising events
- Greater usable capacity than predicted by constant-current specifications
- Increased confidence in meeting lifetime targets
This recovery effect is particularly beneficial for low-duty-cycle applications such as BLE asset tracking and temperature logging.
7 Shelf Life and Stability
Many applications require long shelf life before activation. Zinergy’s printed batteries typically show 10% capacity loss per year, providing predictable performance for products that may be stored or shipped long before use.
If long shelf life is critical, it is good practice to add a capacity margin (e.g. 10%) to your design calculations.
8 Practical Design Checklist
When selecting a battery for your BLE device or logger, we recommend:
- Confirming the minimum input voltage of your BLE chipset at the intended transmit power.
- Checking the peak pulse current draw during transmission.
- Calculating the instantaneous voltage drop using the battery’s internal resistance.
- Ensuring sufficient voltage headroom across the entire discharge curve.
- Verifying capacity against your required operating lifetime and duty cycle.
- Allowing margin for shelf life and temperature effects.
9 How Zinergy Can Help
Zinergy has years of experience developing batteries for RFID, BLE, Sigfox, LoRa, Wi-Fi, and LTE devices. Whether you are using our standard products or need a battery tailored to your specific application, our team is always available to help you select the best solution.
Choosing the right battery early in the design process can dramatically improve performance, reliability, and total cost—so it’s well worth getting it right. If you have any questions, get in contact at: [email protected]
