Two numbers, and why they are far apart
We publish two battery figures, and buyers sometimes assume one of them is a typo.
- Internal sensors: 5 to 6 years or more.
- External sensors with a CR1632 cell: at least 2 years.
Both are real, and the gap is not a mistake. It comes from three things: the size of the cell that fits, the temperature the cell lives at, and how hard the radio has to work. Understanding those three tells you which number applies to your machine — and, more usefully, what you can do about it.
What actually drains the battery
Transmit duty cycle. This is the dominant term. A sensor wakes, measures, and transmits on a shared 433.92 MHz channel. Our default data period is 500 ms, software-configurable. Halving the transmit rate does far more for battery life than any other single change — which is why the data period is configurable rather than fixed. The trade-off is detection latency: a slower period still catches a leak, just with less time resolution.
Temperature. Primary lithium cells lose capacity faster at both ends of the range. An internal sensor rated to +125 °C spends its life in the air chamber of a tire that can genuinely reach that, and heat accelerates self-discharge. The external sensor's −20 °C to +85 °C rating sounds narrower, but in exchange its cell sits in ambient air.
Radio conditions. When the link is marginal, transmissions get repeated and the receiver works harder. This is one practical reason repeater planning matters on long machines: a well-covered wheel transmits less than a wheel at the edge of range. On our 160-wheel beam carrier production configuration, two receivers and twelve repeaters cover 160 sensors; the repeaters are there for coverage, and coverage is also a battery decision.
Electronics overhead. Measurement, processing and wake-up cycles consume something, but on a well-designed sensor they are a small fraction of the radio budget. If a supplier cannot tell you roughly how their life figure splits between radio and standby, they are repeating a number rather than understanding it.
The internal sensor: 5 to 6 years or more
The internal sensor wins on battery because it can carry a larger cell and because the sealing is designed for a long, untouchable life. IP68 sealing, a −40 °C to +125 °C rating, and a cell sized for years rather than months.
The catch is service access. Replacing an internal sensor means breaking the tire off the rim. Nobody should plan a maintenance schedule that depends on doing that on short notice across a fleet of 200 wheels.
So plan it the other way round: replace internal sensors with the tire, not after the battery. Match sensor life to your tire change interval and to your shop's season, and the battery number stops being a risk.
The external sensor: at least 2 years, replaceable in minutes
The CR1632 in an external sensor gives at least two years, and that figure assumes normal ambient conditions and the default data period.
The advantage is not only cost. It is that a flat battery is a five-minute walk-around, not a workshop slot. For fleets that deploy quickly, that matters more than the headline number. It is also why the same cell family is used on our motorcycle platform: an external CR1632 sensor that a rider or a dealer can service without any tooling.
Two things to watch. First, external cells sit in the weather, so the low-temperature behaviour you will see in a cold yard is the behaviour of the cell, not a fault. Second, a sensor exposed to impact or washdown can fail mechanically long before the cell is empty — check the housing, not only the voltage.
Turning "years" into a maintenance plan
A battery figure is a design input, not a schedule. Convert it like this:
- Establish the real conditions. What is the ambient range? What data period will you configure? Is the machine washed down hot?
- Check the test conditions behind the number. Ask at what temperature and what period the figure was derived. A number without conditions is a slogan.
- Add margin, then automate the warning. Configure the low-battery alarm to fire with enough margin that it lands in a planned service window rather than in the middle of a shift.
- Write the replacement into the plan. External sensors: add a battery step to the existing walk-around. Internal sensors: add sensors to the tire change.
- Log the actuals. If a machine eats batteries faster than the paper figure, that is data — usually a sign of temperature or of a marginal radio link, both of which are fixable.
Low battery is a system behaviour, not just a flag
How a system behaves when a sensor gets weak matters as much as how long it lasts. Three things to insist on.
The alarm must be early enough to act on. An alarm that fires when the cell has days left is a nuisance; one that fires with weeks of margin is a plan.
A weak sensor should not look like a flat tire. The system has to distinguish "low battery" from "low pressure", or your operators will learn to ignore both.
The ID mapping must survive the swap. When a sensor is replaced, the new ID has to be bound to the same wheel position in the same configuration file, or the machine's history breaks. If you change batteries every two years across three hundred wheels, that is three hundred opportunities to lose your data.
Cold weather, honestly
Primary lithium cells deliver less energy at low temperature. A sensor rated to −40 °C will still operate, and a cold morning may show a lower battery reading that recovers as the tire and the sensor warm up. That is normal chemistry, not a defect, and it is one more reason to leave real margin in the low-battery threshold instead of setting it at the last possible moment.
What we verify
We run battery power consumption testing and powered aging on the electronics. We also verify pressure calibration on every unit, run water immersion, verify radio range, run full wheel-count integration, and verify CAN and serial protocol behaviour. Those are the checks we actually perform, and they ship with the configuration.
See the TR100 sensor and receiver specification for the full data, or the BPU100 motorcycle sensor for the external CR1632 version. If you tell us the ambient range, the data period you want and how the machine is serviced, we will tell you which battery figure applies.