Pic: Battery Monitor Analysis

[gruso]

A new pic has appeared in MWeston's bucket. It's not a hype photo or anything like that, just some info he is sharing with Notaz. But it's going to get studied and discussed anyway, so here's the thread for it.

Battery monitor analysis
A picture for Notaz in the interest of figuring out how the battery app calculates time left. The top screenshot is with the LCD at low brightness, perhaps around 25%. The bottom screenshot is 100% brightness. The clock is 500MHz and nothing is running but the terminal.

To save you the (highly complicated) maths, here's what I think we can draw from this:

• At 500mhz with terminal running and LCD at around 25% brightness, expected* battery life is 732min / 12.2hrs.
• At 500mhz with terminal running and LCD at full brightness, expected* battery life is 588min / 9.8hrs.
• At max load (ie max current draw on battery) expected* battery life is 419min / 7hrs. (Note: this third figure is kind of arbitrary, see MWeston's post below)

*Note that these are the projections of the battery monitor, not actual test results. Although ED did say that the predictions were pretty accurate in his experience (source). Also note, most importantly, that these are the interpretations of a layman (me) and could be shot down at any moment.

Learnings for us mortals: Nothing too new. I think everyone knows that turning the LCD brightness down will save your battery. It's nice to see numbers though; 7hrs at max load is hard to argue with. [edit - Actually we're not clear on what max load actually is.]

Comments / contradictions?

 

[rabidpoobear]

This is pretty awesome, especially since you can close the lid and lose the backlight power draw altogether, so really it'd be hard for it not to last all of a normal day (even if you don't use standby and just close it)

 

[Tom`]

I wonder if that max load includes Wi-Fi or not? 7 hours with wi-fi on would be really good, but there's a lot of room for wi-fi to be a huge power draw...

 

[gruso]

Yeah I'm not sure about the max load thing. My initial interpretation was that it refers to the maximum current the battery is actually capable of delivering, regardless of what is drawing it (in other words, the battery is current limited for safety, and you're hitting that limit). But a quick calculation says that 4000mAh / 7 hours = 571mA max current. I believe we can draw well over an amp, which means I'm reading the data incorrectly.

Like I said, layman here. Let's wait for a scientician.

 

[MWeston]

There is a register in the fuel gauge where you can put a number in to represent what you think the system will use at its peak. The idea is that software can check the time remaining under maximum load to see if it should cut the system off early because if you were to suddenly need that extra current, the battery would be too low to do it and data corruption could occur. Since Pandora can be running at less than 300mA or need 1.5A if you were driving everything all out, this register isn't all that useful. It's more for devices with no chance of jumping around much. The battery warning would trip way too early if it was expecting 5x the current at any moment.

Since there is no real way to know what the ideal value would be other than to put some crazy high number in there (ie: the USB host was being maxed out), I just put some value in that seemed like a good number under hard gaming only. It was probably 600mA based on the readings but I don't remember right now. It doesn't do anything if you don't write software to need it (which we don't) and it can be reprogrammed at any time since we don't seal the gauge for read only.

The most accurate reading based on all my testing is the "TimeToEmptyAtConstantPower" and 12 hours is pretty cool although it dips down to 10ish when playing Hexen 2 (my new favorite) or something using 3D.

 

[gruso]

Interesting stuff, thanks for the clarification MW.

 

[notaz]

The most accurate reading based on all my testing is the "TimeToEmptyAtConstantPower" and 12 hours is pretty cool although it dips down to 10ish when playing Hexen 2 (my new favorite) or something using 3D.

Currently it's reading TimeToEmpty which seems to be more optimistic (as seen in the photos), can change it to TimeToEmptyAtConstantPower if you think it's better (personally I don't have a clue).