The voltage described in the descriptions of the lithium-ion battery 3.7V is the average value of the voltage when discharging from maximum to minimum values
The maximum voltage to which the batteries are usually charged with 4.18 - 4.20 V. Batteries if more - the battery life is sharply reduced, the container decreases. Manages charging controller charging on the motherboard communicator, it also determines the maximum charging voltage. To change the voltage usually you need to overpass the controller. In the topic about communicators, the Rover discussed the problem - in some batch, controllers with high voltage were dripped (it seems 4.23 V) - the batteries began to run. Now the truth appeared controllers in which the basic parameters are programmed. The integrated overvolt in the battery itself is usually calculated for 4.3 V - the battery will not explode, but as a charge limiter cannot be used, only as the last batch protection.
The minimum voltage is 3.4 -3.6 V, it does not make much sense to discharge below - the voltage drops very sharply with discharge, there will be practically no gain. The driver gives the shutdown command, and it focuses not on the voltage, but on the residual charge calculated or received from the battery controller. In order for the 0% value to correspond to the really minimum voltage and periodic calibration is needed (unless the residual charge is simply determined from the voltage-capacity table)
Calibration does not always help - the people simply disables the driver. Then the communicator usually turns off at a voltage of 3.0 - 3.2 V simply from a stress shortage for normal operation. It is equivalent to turning off the computer by pulling the cord from the outlet with all possible problems. It should be taken into account as an increase in the internal convention of the battery with age, which leads to a strong dependence of the output voltage of the battery from the load current and manifests itself in the unexpected self-power of the communicator, for example, when the consumption current is called).
If the battery for some reason is discharged below 3.0 V, there may be problems charging. If during charging the charging controller detects that the voltage on the battery is less than 3V, then first the controller will limit the charging current to no more than 50 mA until the voltage on the battery reaches 3.0V. The mode is limited in time - in this way bad batteries are detected, charging them with a nominal current can lead to cans depressurization (explosion).
The over-discharge protection built into the battery usually disconnects the banks' leads from the external battery leads if the voltage drops below 2.7 - 2.4 V (depends on the type of chip embedded in the controller). There will also be problems with charging - access to the conclusions of the bank itself from the external terminals of the battery when an external voltage is applied goes through current-limiting circuits (several tens of mA) until the bank is charged to the threshold voltage.
It is impossible to discharge the lithium-ion battery below 2 V - if it remains in this state for some time, internal processes make it impossible to continue using the battery (it may explode)

The charging algorithm and the charger itself for communicators differ significantly from the algorithm and charging phones of a number of manufacturers. For example, the Nokia 6700 phone is a whole two charging controller, one charges from the branded "fine" connector, the other from the MicroUSB connector. In the first case, the controller takes the entire current from the memory which this charger can give - the charger operates in the current limitation mode. If you connect a smaller charging - the battery will be charged with this reduced current, and vice versa. For a long time, Nokia branded charging - write 5V and 750 mA and actually gives more than 7B and strongly depends on the current. It turns out to be 5V if the load current is 750 mA, with further increase in current, the voltage drops sharply - the current stabilization mode.
When charging through the microUSB, the algorithm is completely different. Here it is understood that the charger is simply a source of stabilized voltage (which is the power source of the USB port of the computer), which must provide the current requested charging controller. This current no longer depends on the ability ability - it is determined by the charging controller itself (if only the memory could be able to give the TCT). A funny situation - I have a Nokia 6700 perfectly charged from the NTS charger through microUSB, but refused to charge through the adapter and the "thin" connector ("unsupported memory") and vice versa - branded charged through the "thin" and buggy through microUSB.
The communicators use the second option - the charger is just a source of stabilized voltage. Since the communicator must be charged and the USB port immediately imposes restrictions on the voltage and the maximum current that the communicator can consume from an external source (unless you take special measures, which are lower) - a voltage of 5V, a current of not more than 500 mA (according to specifications for USB) .
Some (for example, ASUS P525 - P750) limit consumption to an even lower level of 100 mA (maximum current from USB 1 or a splitter). To enable 500 mA, ASUS receives via the interface data from the computer about the load capacity of the corresponding port and includes the maximum allowable current. Most communicators simply limit the current consumption from the port to 500 mA.
A powerful communicator during operation can consume more than 500 mA, the battery with such a current limitation from the charger will be discharged and not charged. From the memory you could take more current but how to distinguish the connection to the zoom from connecting to the port? Now, in most cases, contacts 2 and 3 (data bus) in the USB connector are simply embedded. So do in ASUS, HTC HD, HTC Max, HTC Diamond2. For example, in HTC D2 if you connect the memory with open contacts 2 and 3, the charging controller will limit the consumption at the level of about 450 mA, if the contacts 2 and 3 closes the restriction will already be about 900 mA. Similarly, HTC HD and HTC Max. HTC X7500 otherwise - there is a need to close the contacts x and 4 in the miniUSB, consumption restrictions are changed similarly. In the standard charging ASUS PXXX, HTC HD, HTC MAX, HTC D2 Contacts 2 and 3 are closed.
It makes no sense to use charging calculated for a current of more than 1A - until I heard about communicators in which the charging controller would limit the current consumption from charging to a level greater than 1A.
Charging from the port is a little different from charging with a charger - only with current, the final charge will be the same. In some communicators, the charging controller will not turn on charging until data is exchanged with the computer (accordingly, the communicator must be turned on and recognized by the BB)

1. Charge controller (a chip on the communicator's motherboard) is only charged with charging the battery and choosing a source for powering the communicator - an external source or a battery. Its task is to form the correct battery charging algorithm - in two stages
Stage 1 - charging with direct current to the voltage limit (about 4.2 V). Switching to the second stage occurs when the battery is charged up to about 85%
Stage 2 - further charging is performed by a smoothly falling current while keeping this voltage constant (4.2 V). Charging continues until the current drops to a value of about 3% of the original (15 -30 mA). This stage takes about an hour.
After that, charging stops completely and turns on again only if the voltage on the battery drops below a certain value or reconnect the external source (but in this case the criterion for fully charging the battery will be performed immediately and charging will stop again). With this algorithm, the battery will be charged as fully as possible regardless of the initial current (it can be different - the communicator is turned on or off when charging, from which source it is connected). The chip limitsconsumption current from an external source:
Current consumption from an external source = battery charging current + current for communicator operation
more resources are involved - the communicator itself consumes more - less charging current remains.
The chip also controls the temperature of the battery - one of the conclusions on the battery is the output of the thermistor located in the battery, and the charge controller determines the temperature of the battery by its resistance. If below 0 degrees or above the set value - chargingby hardware (in the chip of the charging controller) is prohibited.
So The charging controller monitors only the maximum voltage value on the battery, not allowing its exceeds. To what voltage the battery is discharged - it does not care. The only thing is if when charging the controller detects that the battery voltage is less than 3B, then first charging the controller will limit the value of no more than 50 mA until the battery voltage reaches 3.0V. The mode is limited in time - in such a way bad batteries are determined, the charging of which the rated current can lead to depressurization of the bank (explosion). Also, this chip is in no way involved in calculating the degree of charge of the battery.

2. From the output of the charging controller, unstabilized voltage = battery voltage is fed to the chipnutrition manager On the motherboard of the communicator, and already this chip produces several stabilized voltages for powering the nodes of the communicator.
Often, the unstable operation of the communicator or increased consumption is associated with these chips or with their environment (capacitors, diodes, etc.)

3. Battery controller (the one located in the battery itself) is mainly necessary to protect the lithium-ion banks from overvoltage, overdischarge, short circuits, and reverse polarity of the input voltage. Improper use of lithium-ion batteries (unlike other types) can lead to sad consequences PDA batteries (Post # 2713947) , therefore, protection was designed for them in the form of a battery controller.
In many cases (but not always), another chip is added to the battery controller, which is involved in calculating the state of charge of the battery. More about this in the link.Lithium batteries - operating rules (Post # 2730352). Very briefly the essence: the incoming / outgoing charge is measured by a specialized chip in the battery controller and transmits information via a single-wire interface to the host (communicator), the driver calculates and issues%.
If this chip is not in the battery controller, the degree of charge is calculated simply by the voltage - on the motherboard there is an ADC that measures the voltage of the battery and the degree of charge of the battery is calculated from the table wired into the driver.
In most modern communicators, battery controllers have a similar chip. Criterion for determining the degree of charge 100% (and green indicator) is similar to that it is used in the charging controller (on the example of the DS2780 gauge chip): the voltage exceeded the maximum value (the threshold is installed slightly lower than in the charging controller), the charging current is gradually reduced and reaches a minimum level ( The threshold is slightly higher than the current at which the charging controller completely stops charging). Perhaps where other chips of the meter algorithm are used somewhat different. But in any case, the charging controller (only it determines how to charge the battery and when stopping charging) and the degree of charge degree (no way affects the battery charging) is independent of each other. Those. The green indicator does not mean that the charging has completely stopped (with the communicator enabled) and vice versa: the battery can be fully charged and the indicator does not generize anything (helps CP).

Normally, the system responds to the discharge of the battery, the system reacts with a sequential disconnection of power consumption (WiFi, etc.) and shutdown at 0%. The process of measuring the degree of charges is very inertial and does not respond to rapid changes in voltage (while electronics is very sensitive to short-term stress phael). And the larger the internal resistance of the battery, the greater the stress drawdown when loading the load - for example, with an incoming call or receiving data.
U_out= U_emf- I_heatx R_internal
With a small average, the voltage consumption is sufficient,% of the degree of charge of far from critical - but there is a current sharply increase (the incoming call is the current pulse can be very large) with a large inner resistance the voltage is described below the permissible limit, the system is disconnected (or hangs). The internal resistance of a good-lit-ion of the battery does not exceed 0.2 ohms, with age increases to a greater extent than in the batteries of other types. Usually, the greater the battery capacity is less internal resistance. Contact resistance similarly.
How to measure the internal resistance:
For example, what I intended in HTC MAX:
battery charge level 70%
50 mA current consumption - battery voltage 3.917 V
consumption current 362 mA - battery voltage 3.863 V
Internal resistance = (3.917 - 3.863) / (0.362 - 0.050) = 0.173 Ohm

Often, problems with the battery are not caused by the battery bank, but by the glitches of this meter (chip or driver).
The state of battery charging can be assessed by 4 parameters:
1. The maximum voltage on the battery without load is 4.18 - 4.2 V. If less - problems are possible with a charger (low voltage) or with a charging controller on the communicator motherboard
2. Minimum voltage - the voltage at which the communicator is turned off when working with a minimum load. Depends on temperature, usually 3.4 - 3.6 V at room temperature. If more - most likely a problem with the calibration of the meter. It makes no sense to discharge below these values ​​- the voltage drops very sharply, there is no noticeable gain.
3. Internal resistance - on a good lithium ion, usually not more than 0.2 Ohms. It manifests itself in an unexpected self-shutdown of the device with a sharp increase in load (incoming call) with a seemingly sufficient charge level. Depends heavily on temperature - why lithium ion do not work well in cold weather. For example: I arrived at the dacha, it’s cold, the temperature of the communicator as on the street is about 5 degrees, it turned off and does not turn on. He put it to the stove, warmed up to about 40 degrees - turned on and worked for another 45 minutes.
4. The contact resistance of the battery - the body of the communicator. Although they are gilded, it can be increased. It manifests itself similarly to internal resistance, only does not depend on temperature. To clean with an eraser (in no case emery - remove the coating)
Also see item 7 in the topic header.
Knowing the answers to these points, you can say something about the problem: the battery itself is to blame, some programs, or you need to calibrate the meter.
Calibration meter is discussed in the topic.Battery calibration