[Info] Nexus One Extended Battery Recalibration

A quick run-through on the current situation:

Step 1) Obtain Nexus One
Step 2) Realise that Cyanogen ROM 5.06 drains battery faster than normal (around 1.5% per hour standby, 15% p/h in use)
Step 3) Stubbornly refuse to return to stock ROM or apply power saving techniques (article on this coming soon), instead change to overclocked Froyo Test ROM @ 1.13ghz (also article on this coming soon).
Step 4) Purchase cheap 2700mAh aftermarket battery from eBay (nearly double the standard 1400mAh battery, in theory)
Step 5) Drain the battery to zero to initiate recalibration procedure:

OK here’s where things get tricky, some people say that recalibration is necessary when you switch battery capacities or a similiarly dramatic move. The reason being the phone’s built in battery estimations work on a constantly adjusting range of values it gathers from your min and max battery levels. If you suddenly change the battery capacity to something quite large, then it’s quite likely that it will read incorrectly. This does not of course affect the capacity of the battery, but the accuracy of the battery gauge, which thus renders it overly sensitive, shutting your phone down before the battery is anywhere near empty. The calibration procedure generally agreed upon has two parts. The first is to drain the battery to empty, then reboot and use the last bit of battery to enter Recovery loader, then initiate the ‘Wipe Battery Stats’ function. Then charge it fully. In this way, both the min and max limits of the battery will have been recorded by the phone and it should give a more accurate estimation of the remaining voltage.

I charged it up and cranked up the following:

* Screen at full brightness
* Wifi/APN/GPS on
* Navigation active (Google Maps Navigation)
* Bluetooth on and synced to remote speakers
* CPU running at 100% (stress test) using SetCPU
* LED torch on
* Movie playing

I checked back every 15-20 minutes to see how the power consumption was going, and as expected it was chewing through the juice. Around 1% per MINUTE, if the gauge was anything to go by. With the phone auto-shutting down at < 1%, I booted to recovery and left it on the main screen to eke out the last few % of battery. It’s possible that there’s actually half a battery left, but the phone thinks that there is nothing left.

Here is where opinions differ. It’s scientifically proven that draining lithium-ion batteries to near empty is bad for them. You lose long-term capacity, in the region of a few percent. I did this on my laptop (which has a smarter battery than this phone) and it reported a lower capacity. This is why laptops over time degrade in running time, read here for more info: http://www.batteryuniversity.com/partone-12.htm. However, equally bad would be a substantially inaccurate battery gauge, which is why a once-off calibration may be a good idea. Anyway, it’s still in the process of draining, will update on any gains after a few days of use.

Also, random tidbit I found out today, that the capacitive buttons at the buttom are not hard-coded in their sensitivity or position. This can actually be tweaked within the kernel, which may explain why on some ROMs they feel more/less accurate.

UPDATE: After a couple of hours on the recovery screen, the phone is still functioning, so there appears to be still a bit of battery left. However, if booting to ROM, it reads as no battery and shuts off immediately, which brings me to my theory that:

Standard Battery:
A                                B
E================================F
A = What phone thinks is empty battery (correct)
B = What phone thinks is full battery (correct)
E = Battery is entirely empty
F = Battery is entirely full
Extended Battery:
                               A                        B
E=======================================================F

OK, my theory is that with the extended battery, there’s actually a large reserve below what the phone thinks is empty. As such, the ROM will automatically shut down when it thinks its depleted, but in fact, there’s quite a bit more left from the extended battery. This is backed up by the fact that it still has enough power to last a few hours (at least) with the screen on the recovery page. In addition, when I first received the battery, it read as 16% charge. Being that batteries generally ship with around 60-80% charge, this would put it in line for the phone to be thinking it’s at near E, when it’s in fact, only at 60%. Will update more later.

UPDATE 2: Phone wasn’t completely dead last night, still sitting on recovery, but decided to wipe battery stats and let it charge overnight. Took 4 hours to charge to full, unplugged at 9AM. About 30 min of BT headset use, another 30 min of music playing through the headphone jack, 20 min of web browsing, some emails and the battery hasn’t budged from 100% in 3 hours. Either something is very wrong, or something is very RIGHT!

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3 thoughts on “[Info] Nexus One Extended Battery Recalibration

  1. nice post.
    I did with your tutorial and my battery show 2700mAh / 4178mV when 100% full charged.
    But I charge overnight, morning I saw it 100% full, but 1382mAh / 4178mV.

    So, anyway to fix new extended battery for phone. (or how to take the phone remember new empty point, full point of battery)

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