FoxKat, I enjoy your posts and find them very useful, but I have a theory about using your phone right out of the box. We all know how hard it is to refrain from cranking up and playing with our brand new devices. I never can wait, so I plug it in and let it charge to full while I'm getting it set up and playing with it till the cows come home, then leave it on and let it sit while charging to full and beyond. Doing it this way I have never had a battery issue and never even had to replace an Li-ion as yet. My theory is that while the phone is on and plugged in it charges at a bit slower rate while it accommodates the usage. This gives it a slower charge which may actually be a more sustained charge(my theory)and still fills it to full capacity. I don't see any real difference doing it this way as opposed to charging it fully while turned off. Just my .02 from my personal experiences since the LI-ion's have been out and in use.
cbreze, I respect your opinion and also appreciate your complement. As said in another recent post, I prefer to speak not only when I am confident the answer is correct, but also when I have expert opinion and/or scientific evidence to back my claims. That said, I understand why it may not seem like such a big deal, or any deal at all regarding charging with the power off, however for these batteries, the charging process coupled with the metering of the progress are a highly sensitive and somewhat volatile process.
While the battery is being charged, the power it is drawing from the charger as well as the battery's voltage levels are being very closely monitored to watch for a specific "signature" (change in current draw and voltage increase), that these unique batteries exhibit as they reach their full capacity. These slight changes indicate the battery is in the last phase of charging (the last 10% or so), and tell the charger to reduce the charge rate to top off the battery safely, and then once the 100% capacity plateau is reached as specified by the battery manufacturer and the phone manufacturer, the charger shuts down charging altogether.
The problem with charging while the phone is powered on is that the phone may activate one or more processes while the charging is taking place, such as an email or facebook sync, or an incoming call, and the resultant changes in the power the phone draws due to these processes can "fool" the charging and monitoring circuitry into believing the phone has either reached the last 10% of the charge cycle, or it has reached capacity. This can result in the meter setting the charge capactiy flag to 100% when the battery may have significantly less charge. It can also cause the battery to be repeatedly stressed by being pushed at higher charging rates when the charger should either be in the low current phase or off completely.
Also, the comment about charging to "full and beyond" was said I understand for effect, since both you and I know that a battery only has as large a capacity as it was manufactured to have, and can never be electronically pushed or "boosted" to increase capacity from the moment it leaves the factory. It is not a balloon, it's a battery with finite capacity and finite lifespan. How we treat it will determine how much of its original capacity we get with each charging cycle, and for how long it will last and produce usable power.
The following explanation from BatteryUniversity.com confirms what I have said and assures you that you can only depend on a 100% charge if done with the phone powered down. This doesn't mean you have to do this every time, but it shoud be done on an infrequent basis - typically every 1-3 months or ever 40 or so partial charges, followed by using it to the "low battery" signal at 15%, and then a repeat of the powered-off charge. This sets the high charge and low drain flags for the charging and monitoring circuitry and allows the battery meter to more closely report the State of Charge (SOC) as you use it.
Calibration
The fuel gauge has the inherent drawback of needing periodic calibration, also known as capacity re-learning. This is done to correct the tracking error that develops between the chemical and digital battery on repeated charge and discharge cycles. Calibration could be omitted if the battery received a periodic full discharge at constant current followed by a full charge. The battery would reset with each full cycle and the tracking error would be kept at less than one percent per cycle. In real life, however, a battery may be discharged for a few minutes with a load signature that is difficult to capture, then partially recharged and stored with varying levels of self-discharge depending temperature and age.
Manual calibration is possible by running the battery down until “Low Battery” appears. This can be done in the equipment or with a battery analyzer. A full discharge sets the
discharge flag and the subsequent recharge the
charge flag. Establishing these two markers allows SoC to be calculated by tracking the distance between the flags. For best results, calibrate a device in continuous use every three months or after 40 partial cycles. If the device applies a periodic deep discharge on its own accord, no additional calibration will be required. Figure 1 shows the full-discharge and full-charge flags
.
| Figure 1: Full-discharge and full-charge flags set calibration
Calibration occurs by applying a full charge, discharge and charge. This can be done in the equipment or with a battery analyzer as part of battery maintenance.
Courtesy Cadex
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What happens if the battery is not calibrated regularly? Can such a battery be used with confidence? Most smart battery chargers obey the dictates of the chemical battery rather than the electronic circuit and there are no safety concerns if out of calibration. The battery will charge fully and function normally but the digital readout may be inaccurate and become a nuisance.
Some portable devices sit in a charge cradle in the
on position. The current drawn through the device is called the
parasitic load and can distort the charge cycle. Battery manufacturers advise against parasitic load because it induces mini-cycles. The battery is continuously being discharged to 4.20V/cell and then charged by the device. The stress level on the battery is especially high because the cycles occur at the 4.20V/cell threshold.
A portable device must be turned off during charge. This allows the battery to reach the set threshold voltage unhindered, and enables terminating charge on low current. A parasitic load confuses the charger by depressing the battery voltage and preventing the current in the saturation stage to drop low. A battery may be fully charged, but the prevailing conditions prompt a continued charge. This causes undue battery stress and compromises safety.
