A wireless parking detector is buried in or glued to the pavement, sealed against flooding and rated to survive being driven over, yet expected to run for years on a non-replaceable battery. A smart-manhole sensor shares the same story underground: detect a change - a vehicle arriving or leaving, a cover tilting or flooding - and report it only when something happens. This event-driven architecture is the key to long life, and understanding its detection-and-radio duty cycle is the first step to choosing the power source, including where a rechargeable nickel-metal hydride module earns its place at high-turnover or energy-harvesting sites.
Parking detectors sense the disturbance of Earth's magnetic field by a vehicle (some fuse a second technology - radar or ultrasound - to lift detection accuracy above 99%, with calibrated magnetic-only units typically in the 95-98% range). They are built to punishing mechanical requirements: IP68 sealing per IEC 60529 for a flooded roadbed, IK10 vandal/impact resistance per IEC 62262, and a housing rated to around 15 tonnes of vehicle load, across an extreme temperature span that datasheets put at roughly -45 to +85 C. Smart-manhole sensors add tilt, movement and sometimes water-level or gas detection.
Communications are event-driven over LoRaWAN or NB-IoT (with BLE commonly used for local commissioning and service): a typical LoRaWAN unit transmits near 23 dBm and receives at very high sensitivity (around -135 dBm), and commercial products such as a 25,500 mAh IP68/IK10 detector quote roughly five years at a dozen triggers a day, with real-world life ranging from three to nine years and conservative designs reaching beyond ten.
The first animated figure traces the sensor's electrical life. Almost all the time it sleeps at microamperes. On a detection duty cycle it briefly powers the magnetometer, samples the field and compares it against a learned baseline - a short, low-energy pulse repeated often enough not to miss a parking event. When the field crosses the occupancy threshold (or a manhole tilts), the MCU wakes fully, debounces the event, and transmits an uplink - an event-driven radio burst that is the largest current in the profile, with a brief receive window for acknowledgements and downlinks. BLE commissioning adds an occasional, higher-duty service session.
Because the radio is used only on a state change rather than on a fixed schedule, life is governed less by the clock and more by the number of vehicle events per day and the detection sampling rate - which is why the same hardware lasts a decade in a low-turnover resident bay and half that at a busy loading zone.
The second figure quantifies the trade: with fixed stored energy, field life falls as events per day rise, because every occupancy change carries a radio burst and every burst a fixed protocol overhead, while the background detection sampling sets a floor that never goes away. Operators therefore tune detection sensitivity, debounce time and uplink policy (report on change, periodic heartbeat, and confirmations) as much to manage battery life as to manage data traffic.
At high-turnover sites - commercial decks, drop-off zones, loading bays - the event count climbs high enough that a primary-battery-only design becomes marginal, and a rechargeable architecture with energy harvesting (a small solar or kinetic element on above-ground or gateway-adjacent installations) or a serviceable, replaceable pack becomes attractive.
The default for a buried, sealed, low-turnover detector is a 3.6 V primary lithium pack - some 27 Ah in high-capacity designs - valued for energy density and shelf life. Its limitations are familiar: rising impedance and passivation with age and at the cold extreme (-45 C is well below the comfort zone of many chemistries), and a finite, non-renewable energy budget that cannot recover from an unexpectedly busy site. The radio and magnetometer peaks benefit from a low-impedance reservoir, exactly as in utility meters.
A sealed NiMH module is the right answer in three cases: as a low-impedance pulse reservoir beside the primary lithium for clean radio bursts in the cold; as the rechargeable store in a sensor that harvests energy or is recharged during service; and as the replaceable pack in accessible housings. NiMH discharges reliably at low temperature, cycles through the event bursts for years and uses an aqueous chemistry that is safe inside a sealed, pavement-baked housing.
Smart-manhole sensors - tilt, movement, overflow and sometimes gas - are event-driven in the same way but with far fewer events (a cover should almost never move), so their life is dominated by the periodic heartbeat and the detection sampling rather than traffic. Here the design emphasis shifts to extreme long-term standby, IP68 in a flooded chamber, and the guaranteed alarm burst when the rare event does occur, often after years of silence. A primary lithium cell with a small NiMH pulse reservoir guarantees that the one critical uplink - 'cover opened' or 'chamber flooding' - gets through despite years of passivation.
In both parking and manhole applications, BLE commissioning must be budgeted separately: a long configuration session draws far more than years of heartbeats, and service procedures should be designed not to drain the field battery.
The brief records the detection sampling duty, the expected events per day and their distribution, the radio technology and transmit power, the heartbeat interval, the BLE service model, the mechanical and temperature rating and any harvesting. Paper B turns these into an energy budget and a primary-versus-rechargeable decision; Paper C maps the design onto IP68/IK10, wide temperature and the cell-level evidence.
Weijiang Power supplies sealed nickel-metal hydride cells and rechargeable buffer modules for wireless parking-detection and smart-manhole sensors. Tell us your detection sampling duty, events per day, radio technology, mechanical and temperature rating and whether energy harvesting is used, and our engineers will design a welded, cold-capable NiMH module or replaceable pack with charge management and protection. See formats on the products page.
