Battery usage benchmarking?

[kodiak799]

I'm curious, though I suspect I know the answer...Although I'm sure this thread could be an epic fail.

Anyway, I propose this as an apples-to-apples thread that might provide some insights.

Here is the approach: I use battery left widget and it reports voltage. A full charge for me is usually about 4190mV (have seen it over 4212 - I think max might be 4230 - but plugged in to AC it stops charging at some point and begins to bleed slowly).

So, I go mark the mV used and then go into usage settings...here is what I get:

3863mV...call it 327mV used. I just changed kernels and not getting accurate readings yet, but system says 70% and battery left says 80%. Below I use usage % to estimate mV eaten by the task

5 hours on the button (BB0.4, Chevy ULV 1.2) :
1) display (min brightness), 5 hours on 84% = 275mV = .92mV/min

2) Sweeter Home 6% (29.08 minutes total CPU) = 19.6mV = -.67mV/min

3) Wi-Fi 5 hours 5% = 16.4mV = 0.055mV/min *this needs some work, since browsing would increase wifi usage, or maybe it will show as browser usage

4) cell standby 5 hours 4% = 13.1mV = 0.044mV/min

5) android system (4.27 minutes total CPU) = 6.5mV = 1.53mV/min (for fun, 1.26KB sents, 825bytes received).

Yeah, almost no real usage. I'll do a full charge tonight and then tomorrow have a better mix with idle, voice, browsing, etc...

People may say the voltage reports are inaccurate, but to me I feel like the proper mV per numbers should establish some decent benchmarks to find some more efficient apps / roms and ways of running your phone

 

[tonydelite]

You're confusing amps with volts.

Battery capacity is measured in mAh (milliamp hour).

Volts are not an indicator of how much power is left in a battery... especially a lithium based chemistry like the battery used in the Droid. Lithium batteries have a fairly flat discharge curve.

 

[kodiak799]

You're confusing amps with volts.

OK...is the methodology not sound? It's reported as volts by Battery Left. I haven't seen anything reporting mAh

Obviously it won't go to 0 on mV, but won't the phone die about the same point, so shouldn't the mV used be a decent proxy for usage/capacity especially if it's a flat discharge curve?

 

[tonydelite]

No, the methodology is not sound. A lithium polymer battery like the one in the Droid is probably going to be somewhere around 4.2V (4200mV) fully charged and 3.0V (3000mV) fully discharged. The majority of time, it is going to hover somewhere in the middle, hence the nominal voltage rating of 3.7V

 

[tonydelite]

The mAh rating is a rating of capacity... so if the stock Droid battery is rated for 1300mAh, that means it could withstand a constant 1300mA draw for a solid hour before the battery is fully discharged. It could handle 650mA for 2 hours, 325mA for 4 hours, etc.

 

[kodiak799]

No, the methodology is not sound. A lithium polymer battery like the one in the Droid is probably going to be somewhere around 4.2V (4200mV) fully charged and 3.0V (3000mV) fully discharged. The majority of time, it is going to hover somewhere in the middle, hence the nominal voltage rating of 3.7V

But Battery Left reports a mV that discharges in a mostly linear fashion, it doesn't hover around a constant and it doesn't bounce around.

Or, if I understand correctly, your saying sometimes my battery will fully discharge 500mV and other times could be 800? So I guess I understand the flaw. Back to the drawing board I suppose.

 

[tonydelite]

You're sort of on the right track...

There might be periods during the battery's discharge cycle that APPEAR to be a linear drop in voltage with a constant load, but it won't be all the time. Like I said before, your Ceiling is 4.2, your floor is 3.0 or so. (it might go a little lower.) If you are fully charged and apply a certain load, you might see your voltage rapidly drop from 4.2 to 3.9 or 3.8v but it wont continue to drop at the same rate even if the load remains constant.

 

[kodiak799]

If you are fully charged and apply a certain load, you might see your voltage rapidly drop from 4.2 to 3.9 or 3.8v but it wont continue to drop at the same rate even if the load remains constant.

Thanks for the insight....I still feel like varied use over time should average out the issue you mention....One cycle may not be apples-to-apples to another cycle, but 10 or 20 cycles would seem to be a decent proxy for comparing averages.

I don't know if battery left is basing it's % on mV, but the % seem to be pretty consistent. If I do a full discharge, it seems like you should be able to calculate mV as that % x 1200, and calculate what that works to on a /min basis. Call it whatever you want, if the % of battery are accurate, then everyone has 100 units and that works out to some unit/min for each function/app. Maybe drop the mV and just talk in terms of 100 units (which is 100%, I'm just recognizing % is not created equal and the usage is actually unit/min usage).