Schlage Lock Battery level

[mikek]

Is there any way to read voltage rather than percentage in the battery level field? I found the following on the Schlage site:

 

"4.7V will trigger the low battery response."

"4.4V is when the lock stops operating."

 

I just talked to Schlage customer support, and was told that there's not a strong linear relationship between voltage and percentage. They said that the low battery warnings typically appear in the 50-60% range, but they have experienced warnings both below and above that range too. So percentage, to me, seems of little value other than as a general indication of health. Assuming that 100% would equal 6V (or even 6.4V), the 50-60% value makes no sense. I asked if it was possible to directly read voltage, and they didn't know, so I'm thinking if anyone has been able to figure that out it has to be someone here.

[stusviews]

The battery must be tested under load. The more to the enrgy available than just voltage which is why a voltage reading is useless. The %age of life left is an estimate of the ampacity remaining, closely related to power (watts). Thus, %age is the best warning.

 

BTW, a battery without a load can give nearly a full voltage reading without being able to supply power to operate something. Battery testers, but not voltmeters, actually put a load on the battery and show %age, not volts.

[mikek]

The battery must be tested under load. The more to the enrgy available than just voltage which is why a voltage reading is useless. The %age of life left is an estimate of the ampacity remaining, closely related to power (watts). Thus, %age is the best warning.

 

BTW, a battery without a load can give nearly a full voltage reading without being able to supply power to operate something. Battery testers, but not voltmeters, actually put a load on the battery and show %age, not volts.

 

True that the battery must be tested under load, but a resistor in the measurement circuit satisfies that requirement. If Schlage comes right out and identifies the two voltages at which the low battery warning alarms and the lock stops functioning, then it's safe to assume that a resistor already exists in the internal circuitry. If that's the case, then there's no reason that test result (battery voltage under load) can't also be an output variable (even if only periodic). To me, that would be a much more useful value that something vague like percentage of life remaining (with an equally vague limit of 50-60%).

 

I've never heard the term "ampacity" used as a measurement of battery capacity.  

[mwester]

I've never seen a device that actually has a load resistor and associated circuitry to switch that resistor into the circuit when the voltage is measured -- it's only ever measured when the device is awake and running.  I've also never seen a vendor publish the voltage at which the device will cease functioning separately from the voltage at which the device will signal "low voltage" -- I suspect the engineering team has a set of statistics that can determine the "typical" failure voltage, and I suspect that the "low voltage" threshold is set somewhat higher, but that's just a guess since I've never seen any consumer device publish that.

 

In other words, this is a consumer device, and I suspect the questions you are asking have no published answers.

 

And regarding voltage vs capacity -- there's a lot of studies on that, and for any given production run of a specific battery, there's almost certainly a good way to characterize that (assuming a properly calibrated load resistor and measurement circuit).  But given that a consumer device almost certainly does NOT have a precise load resistor (in fact, highly unlikely it has any load resistor or other means of ensuring a known calibrated load while measuring, since if you think about it, the device itself is a load while it is measuring, and that's pretty variable), and given that it's highly unlikely that the device's measurement circuit is very precise or accurate (especially considering that the environment factors such as temperature are pretty variable), combined with the fact that the vendor has no control over which battery you've installed, the truth is that any "low battery" signal is nothing but a wild guess!)

 

For critical devices - do like smoke alarms, and just replace them periodically whether they need it or not.  JMO.

[mikek]

I've never seen a device that actually has a load resistor and associated circuitry to switch that resistor into the circuit when the voltage is measured -- it's only ever measured when the device is awake and running.  I've also never seen a vendor publish the voltage at which the device will cease functioning separately from the voltage at which the device will signal "low voltage" -- I suspect the engineering team has a set of statistics that can determine the "typical" failure voltage, and I suspect that the "low voltage" threshold is set somewhat higher, but that's just a guess since I've never seen any consumer device publish that.

 

In other words, this is a consumer device, and I suspect the questions you are asking have no published answers.

 

And regarding voltage vs capacity -- there's a lot of studies on that, and for any given production run of a specific battery, there's almost certainly a good way to characterize that (assuming a properly calibrated load resistor and measurement circuit).  But given that a consumer device almost certainly does NOT have a precise load resistor (in fact, highly unlikely it has any load resistor or other means of ensuring a known calibrated load while measuring, since if you think about it, the device itself is a load while it is measuring, and that's pretty variable), and given that it's highly unlikely that the device's measurement circuit is very precise or accurate (especially considering that the environment factors such as temperature are pretty variable), combined with the fact that the vendor has no control over which battery you've installed, the truth is that any "low battery" signal is nothing but a wild guess!)

 

For critical devices - do like smoke alarms, and just replace them periodically whether they need it or not.  JMO.

 

Thanks. I agree, and I found it strange that those values were published as well. But since they were, I thought it would be nice to take advantage. It's certainly not necessary, and I have no problem doing an annual change. I just don't like arbitrary limits and meaningless data, so I'll just learn to live with it and move on to something else.