question: Why do batteries work a bit longer when switched around?
comment: If the voltage is getting low, any bit of electrical resistance you can get rid of helps maximizing the voltage the device gets. Even just taking them out and putting back can scrape a bit of corrosion from the end caps of the cells and the contacts in the device. Plus resting the batteries, even briefly while switching them round can let the internal chemistry relax a little. Charge that builds up dissipates.
passages: Even just a single string of batteries wired in series can have adverse interactions if new batteries are mixed with old batteries. Older batteries tend to have reduced storage capacity, and so will both discharge faster than new batteries and also charge to their maximum capacity more rapidly than new batteries.
   A common process often discribed to memory effect is voltage depression. In this case, the peak voltage of the battery drops more quickly than normal as it is used, even though the total energy remains almost the same. In modern electronic equipment that monitors the voltage to indicate battery charge, the battery appears to be draining very quickly. To the user, it appears the battery is not holding its full charge, which seems similar to memory effect. This is a common problem with high-load devices such as digital cameras and cell phones.
   Manufacturers often engineer their optical mice—especially battery-powered wireless models—to save power when possible. To do this, the mouse dims or blinks the laser or LED when in standby mode (each mouse has a different standby time). A typical implementation (by Logitech) has four power states, where the sensor is pulsed at different rates per second:
  
  BULLET::::- 11500: full on, for accurate response while moving, illumination appears bright.
  
  BULLET::::- 1100: fallback active condition while not moving, illumination appears dull.
  
  BULLET::::- 110: standby
  
  BULLET::::- 12: sleep state
   Section::::Voltage considerations.
   Voltage depression is caused by repeated over-charging of a battery, which causes the formation of small crystals of electrolyte on the plates. These can clog the plates, increasing resistance and lowering the voltage of some individual cells in the battery. This causes the battery as a whole to seem to discharge rapidly as those individual cells discharge quickly and the voltage of the battery as a whole suddenly falls. This effect is very common, as consumer trickle chargers typically overcharge.
  
  Section::::Other problems perceived as memory effect.:Temporary effects.:Voltage depression due to long-term over-charging.:Repair.
   In a subcircuit, switching will change the load current drawn from the source. Typical power supply lines show inherent inductance, which results in a slower response to change in current. The supply voltage will drop across these parasitic inductances for as long as the switching event occurs. This transient voltage drop would be seen by other loads as well if the inductance between two loads is much lower compared to the inductance between the loads and the output of the power supply.
   As a mixed string of new and old batteries is depleted, the string voltage will drop, and when the old batteries are exhausted the new batteries still have charge available. The newer cells may continue to discharge through the rest of the string, but due to the low voltage this energy flow may not be useful, and may be wasted in the old cells as resistance heating.
   Memory effect
  
  Memory effect, also known as battery effect, lazy battery effect, or battery memory, is an effect observed in nickel-cadmium and nickel–metal hydride rechargeable batteries that causes them to hold less charge. It describes the situation in which nickel-cadmium batteries gradually lose their maximum energy capacity if they are repeatedly recharged after being only partially discharged. The battery appears to "remember" the smaller capacity.
  
  Section::::True memory effect.
   This is usually a function designed into the protocol that allows this to happen - most notably how the transmission is structured - for example in slots with headers containing address details so that devices can listen to these headers in each slot to decide whether the transmission is relevant to them or not. In this case, the receiver only has to be active at the beginning of each slot to receive the header, conserving battery life.
   In the most basic of circuits, if the current falls below the holding current even briefly, the circuit is turned 'OFF' (becomes blocked). However, complex circuits and devices may have different delays built-in between the time the current falls below this level and the time the device turns 'OFF'. Whether a device turns 'ON' when current is restored is a design issue. The current necessary to restore the circuit to the 'ON' state, called the "threshold current" (See threshold voltage), may be much greater than the holding current, or only very slightly more. Nevertheless, where the device is designed to turn back 'ON' upon restoration of the current and where the device is running at or about the holding current level, slight variations in the current can cause "flicker" as the device cycles 'OFF' and 'ON'. If flicker is undesirable, it can be reduced by the use of capacitors or other circuits, on the other hand, flicker can be used to measure small events as in a Geiger–Müller tube.
   BULLET::::- When turning on from the off state, I depends on the voltage across the two main terminals MT1 and MT2. Higher voltage between MT1 and MT2 cause greater reverse currents in the blocked junctions, thus requiring less gate current to trigger the device (similar to high temperature operation). In datasheets I is generally given for a specified voltage between MT1 and MT2.
   NiCd cells, if used in a particular repetitive manner, may show a decrease in capacity called "memory effect". The effect can be avoided with simple practices. NiMH cells, although similar in chemistry, suffer less from memory effect.
  
  Section::::Lifetime.:Environmental conditions.
   If a battery has been completely discharged (e.g. the car lights were left on overnight) and next is given a fast charge for only a few minutes, then during the short charging time it develops only a charge near the interface. The battery voltage may rise to be close to the charger voltage so that the charging current decreases significantly. After a few hours this interface charge will spread to the volume of the electrode and electrolyte, leading to an interface charge so low that it may be insufficient to start a car.
   Looking at C2, just before Q2 turns on, the left terminal of C2 is at the base-emitter voltage of Q1 (V) and the right terminal is at "V" (""V"" is used here instead of "+"V"" to ease notation). The voltage across C2 is "V" minus "V" . The moment after Q2 turns on, the right terminal of C2 is now at 0 V which drives the left terminal of C2 to 0 V minus ("V" - "V") or "V" - "V". From this instant in time, the left terminal of C2 must be charged back up to V. How long this takes is half our multivibrator switching time (the other half comes from C1). In the charging capacitor equation above, substituting:
   Section::::Memory effect.
   When this might cause a problem, remote sense can be used to force the power supply to counteract the voltage drop by raising the voltage at its output terminals. If successful, it will exactly cancel the drop along the leads, yielding the correct voltage at the input terminals of the load. This is accomplished by using separate "sense leads," connected to the load's input terminals, to measure the output voltage. (Because the sensing function draws only a very small amount of current, there is practically no additional voltage drop due to the sense leads themselves.)
   The four options make use of various physical phenomena and thus offer a variety of signal processing to overcome:
  
  BULLET::::- multipath propagation,
  
  BULLET::::- crinked and direct paths
  
  BULLET::::- multipath fading
  
  BULLET::::- excess reach of nearby colliding transmitters
  
  BULLET::::- higher populations of transmitters
  
  The two-factor concept fails if both items get lost at the same time without raising an alarm, or if one of the batteries is below operational stage or is simply inactive.
  
  Section::::Usage principle.
   When recharged, the old cells recharge more rapidly, leading to a rapid rise of voltage to near the fully charged state, but before the new cells with more capacity have fully recharged. The charge controller detects the high voltage of a nearly fully charged string and reduces current flow. The new cells with more capacity now charge very slowly, so slowly that the chemicals may begin to crystallize before reaching the fully charged state, reducing new cell capacity over several charge/discharge cycles until their capacity more closely matches the old cells in the series string.
   For this to work, the cell capacitance must be higher than the electrode capacitance by at least an order of magnitude. Capacitance slows the kinetics (the rise and fall times) of currents. If the electrode capacitance is much less than that of the cell, then when current is passed through the electrode, the electrode voltage will change faster than the cell voltage. Thus, when current is injected and then turned off (at the end of a duty cycle), the electrode voltage will decay faster than the cell voltage. As soon as the electrode voltage asymptotes to the cell voltage, the voltage can be sampled (again) and the next amount of charge applied. Thus, the frequency of the duty cycle is limited to the speed at which the electrode voltage rises and decays while passing current. The lower the electrode capacitance the faster one can cycle.
   A hysteresis is sometimes intentionally added to computer algorithms. The field of user interface design has borrowed the term hysteresis to refer to times when the state of the user interface intentionally lags behind the apparent user input. For example, a menu that was drawn in response to a mouse-over event may remain on-screen for a brief moment after the mouse has moved out of the trigger region and the menu region. This allows the user to move the mouse directly to an item on the menu, even if part of that direct mouse path is outside of both the trigger region and the menu region. For instance, right-clicking on the desktop in most Windows interfaces will create a menu that exhibits this behavior.
   Complete discharge of multi-cell packs can cause reverse polarity in one or more cells, which can permanently damage them. This situation can occur in the common arrangement of four AA cells in series in a digital camera, where one completely discharges before the others due to small differences in capacity among the cells. When this happens, the good cells start to drive the discharged cell into reverse polarity (i.e. positive anode/negative cathode). Some cameras, GPS receivers and PDAs detect the safe end-of-discharge voltage of the series cells and perform an auto-shutdown, but devices such as flashlights and some toys do not.
   Similarly, impedance in the power supply can couple input to output and cause oscillation. 
  
  When a common power supply is used for several stages of amplification, the supply voltage may vary with the changing current in the output stage. The power supply voltage changes will appear in the input stage as positive feedback. An example is a transistor radio which plays well with a fresh battery, but squeals or "motorboats" when the battery is old. 
   The commutating d"v"/d"t" rating applies when a TRIAC has been conducting and attempts to turn off with a partially reactive load, such as an inductor. The current and voltage are out of phase, so when the current decreases below the holding value, the TRIAC attempts to turn off, but because of the phase shift between current and voltage, a sudden voltage step takes place between the two main terminals, which turns the device on again.
  
  In datasheets, this parameter is usually indicated as formula_4 and is generally in the order of up to some volts per microsecond.
   Limited*=supported, but does not allow USB re-enumeration, which not only causes long delays in switching, but also sometimes causes HPD (Hot-Plug Device) errors to the OS system(s).
  
  Yes*=Latency time within 1 second while switching between channels/ports.
  
  Section::::Use.
   If the needle reads "fast," then the plant's generator is slowed down by a very small amount and the needle turns counterclockwise (toward the zero mark). Alternatively, if the needle reads "slow," then the plant operator speeds the generator up slightly, and the needle turns clockwise. Slightly before the needle reaches the zero mark, the plant operator returns the generator to the grid frequency in order to stop the needle when it reaches the zero mark. When the needle is at zero and is not moving, the two systems are synchronized.
  