📄 How often will I need to change dispenser batteries?
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How often will I need to change dispenser batteries?


As you might expect, this answer is not set in stone.

Each Mirador Guardian™ dispenser runs on 4 C-cell batteries. The battery life of a given unit will vary depending on dispenser configuration, usage/activity pattern, Wi-Fi signal strength & stability, battery brand/model, and liquid type. Below we’ve provided some details on why we measure in the ways that we do, getting to know your facility's use patterns, and recommendations for monitoring.


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Battery Behavior

Batteries do not drain in a static/volume way, like for example how ABHR or soap liquids do.  

As noted in Alert Level Indicators, the Low status indicates that the power draws from the dispenser are becoming inconsistent, and that a battery change will be required soon.  

  • An array of unpredictable behavior begins to occur once a low capacity is reached. Unpredictable behaviors increase the potential for sanitizations or check-ins to be skipped, as the dispenser cannot complete the handshake to the application, which ultimately lowers our confidence rate for compliance overall. 
  • If the Last Message Time indicator is red, meaning that it is offline, no updates from the dispenser are being communicated to the application. Dispensers will continue to dispense liquid even when they fall offline and no longer report their activity to the cloud.  This means that users can continue sanitization, and ensures coverage for infection reduction, during times when the internet might go down due to emergency or other unforeseen outages.  
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Replacing batteries before full depletion - when they reach Critical low voltage, versus when they cease performing - directly impacts reporting & data accuracy. 

 

Tech Team Moment!
We use 4x alkaline Type-C cells which, under zero load conditions, are considered depleted when they each reach ~0.9V. So, for a 4x cell configuration that is ~3.6V.
Of course, we don’t operate in zero load conditions. Nominally, there is a steady – albeit very low (~0.6mA) – current draw in quiescent state for Gen-2 dispensers.
Then, when a dispense occurs, the energy needed to drive the pump effectively demands ~400mA for durations of up to 0.7 seconds when the battery is low (~5.0V-5.3V). Alkaline cells cannot handle this kind of current draw at that point. Doing so causes the battery voltage to temporarily plummet to ~4.0V. This recovers after a short time (relaxation period).
Towards the end of a battery’s lifecycle, its terminal voltage can often relax all the way back to ~5.4V when at rest, but still not have sufficient charge (electrons) left in its chemistry to run the motor during dispense events. In this state, attempting to drive the motor can cause the battery voltage to (temporarily) dip so low that the dispenser goes through a reboot and loses the Wi-Fi connection. The reboot process, including needing to reestablish the Wi-Fi connection, drains the battery even more.
In Summary: The 5.0V threshold we use to flag critical battery is already at the ‘edge’ of its operating conditions with almost no headroom or margin. Replacing batteries in Low status, or as soon as possible once they’ve hit Critical status, is advised.


Ideally, batteries should always be replaced before they die completely.


 

Expected Run Times

Our team tests the dispensers based on expected usage pattern and dispenser configuration, not time, because the span between battery changes will be highly variable depending on the factors above. For reference, we have provided a Patient Room example below, which you can use to compare against the trends observed at your facility:

  • 4 motion triggered wake-up events every hour during 'waking time' (16 hours), 0.5 events/hr otherwise. To wit, 68 motion events/day.
  • 3 dispense triggered wake-up events every hour during 'day shift' (8 hours), 0.5 events/hr otherwise. To wit, 32 dispense events/day.
  • Each wake-up lasts, on average, 15 seconds.

Under this model, the battery estimate is 184 days (6 months) assuming no HTTP retries and no Wi-Fi disconnects.  

The battery life estimate is highly sensitive to assumptions around what fraction of a given day the dispenser will be 'awake' (i.e., not in power saving mode). This primarily includes wakeups triggered by motion and/or dispenses. Wake-up durations could be short (e.g., few secs due to patient turning around in their bed) or long (e.g., multiple minutes if someone visits the bed).  


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Public Area dispensers, like those in hallways, tend to have far more dispense events per day.  However, they do not trigger motion sensing scans, and so do make up for battery consumption in that way.  Power consumption, then, for Public Area dispensers will depend on how "popular" that dispenser is, i.e. where it is placed based on foot traffic patterns, etc.  



Monitoring

Because of the (likely significant!) differences in lifespan between high-traffic and low-traffic areas, we have taken every opportunity to make the monitoring of the dispensers themselves, and not just compliance, as straightforward as possible. For example:

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In instances where battery voltage oscillates between thresholds, the EMA can display variances between the Battery Status (ex. Dispenser Status Report) and the raw Voltage (V) (ex. Management/Dispensers) readings. These intermediate readings are expected behaviors and are short-lived, resolving themselves as battery life declines further into each threshold.


Using these tools holistically, across all of your multi-functional teams ensures that your dispenser network is optimized and running smoothly 24/7, and that your teams are aware of general use patterns - as well as when those patterns change!