Hello Guy!
I guess the question is this , are mine just worn out from time and use. I know this can happen and sounds like the case.
Yes, I suppose - in your language - your batteries are "worn out". But the reason why is not so easy to describe. Such a battery is in fact an electrochemical system, which is mainly temperature dependent in all its properties, which are 'internal resistance', 'free diffusion of iones' and at last the result of the Nernst equation (temperatur dependency of the voltage of a cell).
The biggest missbenefit is the internal resistance of the electrochemical cell. This resistance is a parasitic load which consumes energy inside the cell only (produces heat). According to the law of Ohm, this internal resistance decreases the useable cell voltage between its two output electrodes. If a load is applied to the output (in our case the M8
, depending on the working state of the camera, a certain current is flowing. Our friend Ohm tells us exactly (U = I x R), how much volts we loose in the cell itself. The bigger the current, the bigger the lost voltage. And of course, the bigger the internal resistance of the cell, the bigger the lost voltage again.
So - as a first approach - all we have to fight against, is the internal resistance. This internal resistance is a function of more than one physical and/or chemical effect. The mobility of the charge carrier, the macro and micro state of the electrolytical compound, the surface of the internal electrodes are all influenced by charging and discharging and are some of the sources of wearing out. You can compare it with a truck, full with glass bottles (our stored current) and everytime the battery is discharged, we take some bottles from the truck. In the other way, when charging, we put some new bottles on to the truck. You can imaginge, how sensible this would be, to prevent all the glass bottles from breaking. If enough glass is broken, we can not unload all the bottles behind all the broken glas, so we have to think, the truck is empty.
Now when the camera and batteries are not resetting the charge monitors that are in the camera and in the battery gets confused from shallow recharging, but can be reset by a single deep charge.
The great benefit of a Li-Ion electrochemical cell ist, that the present voltage is a (documented) function of the state of charge of the cell. There is no mystery behind the charge monitor, it is a simple voltage meter. Only the degree of charge/discharge has to be defined (once, by the producer) for a given type of cell.
As long as the charge and discharge current is low enough, the voltage/time gradient is constant for the whole lifetime of the cell and we can measure the charge state with very high precision!
The game (of measuring) is quite different, if the charge/discharge current increases to such a value, that the internal resistance of the cell must be included to the voltage/time function (you can verify this by looking into the data sheets of the cells).
A new cell has intentionally a compareable very low internal resistance, the absolut value (unit Ohm, greek capital letter omega) is no absolut constant, but is highly dependent of the manufacturing process and (from the view of the enduser) the quality control. But nevertheless, the internal resistance is always existing and influences the voltage/time gradient of any charge/discharge cycle. And therefor it also influences the min and max voltage of charge/discharge. A slight difference in internal resistance moves significantly the endpoints of charge and discharge.
Now - to finalize - take into account, that your camera consumes different amount of current, depending on ambient temperatur and the momentarly state of usage (cocking the shutter, writing to memory card, holding the solenoid of the shutter curtain and so on).
And according to the above mentioned law of Ohm, the voltage between the two connectors of the batteries differs permanently. The battery monitor is - I assume - working only in distinct intervals and depending on the point of measurement, the voltage may have any value in the range "battery full", "battery partly full" or even "battery empty".
The live with such an device has to extreme limits from "never use" to "use it clever". Your only chance, to have the biggest possible benefit from your battery is, to keep internal resistance as low as possible. One of the best ways in this direction is, to minimize the degree of discharge before recharge. Omit discharge below 50% of the capacity.
Sideproblem: low ambient temperature and resulting low temperature of the electrochemical cell itself. Below 0°C your game is lost prematurly. Your rechargeable battery (secundarly element) converts itself to a primarly element (not rechargeable). The German language differs more precisely (Akkumulator - Batterie) but I hope, the message was transmitted well.
This - limited usablity below 0°C - is mainly a (bad) property of 'non liquid' (gelatinous) electrolyte containing cells.
