Charging Batteries and Ill Effects
Unfortunately, the misbelief is widely spread that the modern batteries (specially the nickel metal-hydrid NiMH) do not have any memory effect any more and/or that all modern chargers can avoid it. Actually, the tendency of this is a decrease in the technological development, but it is still existent, a thing that makes a charger lose in durability and capacity sooner as wanted due to the wrong handling of the charger or lack of knowledge concerning the charger and the possibilities it offers.
The memory effect is when a charger starts to "remember" that only a part of its capacity has been used because it had been loaded much too early (re-loaded) or it had not been loaded completely. If this happens only once or a few times, the charger will tolerate this of course, but the proper loading is essential for the capacity and the durability of the device.
Even though most of the devices do recognize a defective charger or the wrong polarity, one should in any case pay attention to position the batteries in the correct direction. Most of the chargers do - as far as their possibilities allow it - automatically the right thing with the battery, but the user unfortunately does not. Although the modern and specially the Ni-MH standard batteries that are meanwhile in common use do have a less pronounced memory effect (in case of this type it is correctly spoken of a - similarly natured - "lazy-battery-effect"), the battery maintenance should be taken seriously and one should take care of a correct loading (in the right stage of discharge), as far as this is not done by an intelligent charger. By the way, in the case of the lithium-ion batteries there is no memory effect known. One basically has to assume clearly that every battery - no matter which type - loses capacity in the course of its lifetime and will be over-used .
A problem that should not be less estimated is the excessive discharge up to the so-called deep discharge, a thing that damages the battery seriously, takes away almost all of its capacity and that can be only readjusted with some special preparations or devices. It is, for example, absolutely senseless to use some recharcheable batteries for some appliances of low consumption as for example for a wall clock, a LCD display ( e.g. clock, thermometre) or a remote control. These items do need such a small quantity of energy, that the chargeable batteries are over-used to such an extent that they get "emptier than empty".
To the contrary, if the rechargeable battery is fully used with a normal (high energy-consuming) device (e.g. camera, torch, flash unit), a normal discharge takes place and the chargeable battery is discharged in an optimal way for the recharging. This is managed automatically as most of the times, the devices turn off by themselves or do not work anymore if there are not enough reserves in the energy dispensers. Regarding the perfect charging process, the modern and specially the more expensive chargers offer an automatical recognition of the remaining capacity and an eventual automatic refresh function: If necessary, the batteries are discharged up to an optimal level and is not reloaded as usual up to then.
Alternatively, there is a basic possibility to discharche the batteries "manually" to the optimal state of discharge. It is surely completely wrong to simply reload some batteries that are out of use since a longer time period or some that are half discharged (provided the charger is not an intelligent device) without discharging them previously. By this way, the only right way to reload the simple chargers is to get them first emptied by a nomal consuming device as for example a torch, a video light or during a long telephone conversation in order to start rechaging them afterwards.
Re-published from Patrick Wagner.
It is important to consider that often times the charging device itself can illicit the user of the battery's damage from previous charges or age. Batteries can be overcharged, over heated and simply out live there expected usefulness, care should be taken to note the age of the battery and examine its casing to determine if there is added damage the user might not be aware of. Another aspect is the heat generated during the charging: The cooler the battery remains, the less it will be damaged. The fast chargers partly have an additional fan in order to avoid that the temperature goes up uncontrollably. Thus, those who approach the topic of charging and its theory with intelligence and skill will be well off with a more simple charger as long as the charging times and charging currents are respected.