This is some initial information about the Nikon D1's battery and charger. Measurements are being done and detailed information will gradually be added here. Most of this temporary information is from my responses to questions on the different news and mail lists.
The cells in the Nikon battery are not unusual. There are six "4/5 A size" cells. They are shorter and fatter than the typical AA cell. The battery does not contain any fancy electronics, just a thermistor for temperature sensing and a fuse which normally is self-resetting but I have not verified its property.
Note: There is a little plastic projection at the end of the battery that pushes on a switch inside the camera when the battery is inserted. I do not know its function, but it is commonly used to differentiate between different types of battery technology.
The charger is a universal input (100-240VAC) switching type power supply. Presumably, but not verified, the charger uses the negative voltage slope of a fully charged battery to determine when the battery is charged and, again presumably, uses the thermistor for a safety backup. When a NiCad or Ni-MH battery is charged, the voltage gradually increases as the charge builds up until charged when the voltage levels off. As the battery is further charged, the voltage drops very slightly. It is that slight drop that is usually used by chargers to detect a charged battery.
One MH-16 Charger was tested and the following was measured:
By the way, when an empty battery is put on a charger, the energy delivered to the battery gets converted to "chemical" energy and the battery stays relatively cool. When the conversion process is finished and the battery is charged, the electrical energy got to go somewhere; it is converted into heat. That is why batteries get hot at the end of the charging cycle. A simple but effective test: If the battery is getting hot, it is charged.
As a response to a question about using a home built charger or a different brand of charger: If you know what you are doing, you can charge the battery by many methods, specially if you are keeping the charging current low and not rushing the charging. I am sure Nikon would not approve it and you could void any warranty on the battery.
This issue with "refresh" is strange and questionable but if there is some real information available I love to see it. I do not believe that the battery conditioning is necessary at all except possibly during some extreme cases. Most of it stems from old information about battery problems that do not exist today. The rest are marketing ploys: "My charger is better than yours since it has a refresh button."
I am an electronic engineer and I have done several battery charger designs for large corporations and I have done commercial evaluations of Ni-Cad batteries for a battery manufacturer. I also did a computerized production battery tester for them. A friend of mine is a consultant to the battery manufacturing industry and his view echoes mine. I am not trying to brag, just so you know that I have been down this road before.
A long time ago, Ni-Cad batteries used to have a "memory effect." What basically happened is that batteries that were repeatably only partially discharged and then charged, started to "remember" it and they had less capacity when one day requested to deliver all the energy. Typically this happened with a pager, phone or other device that was used daily and the battery was only partially discharged and then charged every night.
Battery manufacturers were well aware of the problem and made drastic improvements in the battery construction and practically, the problem is gone today. Ni-MH is one of the latest ones and should be even better. At one very early point, a few battery manufacturers tried to ship partially finished batteries that required a charge/discharge cycle to be operational. That was quickly discontinued after a lot of customer complaints. I cannot imagine that Nikon would be doing that today.
Some charger manufacturers in the old days added the refresh function to the chargers and it was a useful function at that time in some cases. Later, when not needed, the marketing departments insisted to keep or add them as a sales gimmick. That is the common reason for the refresh function today!
With today's modern rechargeable batteries there is little need to refresh. Hitting the refresh button once in a while is not likely to significantly reduce the life of the battery and might possibly help a tiny bit but to me it is questionable until proven otherwise. Doing it cycle after cycle is not adding any life to the battery plus it extends the time on the charger.
Refresh is basically nothing more than a complete discharge and if you are running the batteries empty each time there should not be any need for extra refresh.
The "memory effect" only happened if day after day the batteries are charged after just a little use. Batteries are typically not used that way in the D1. They are normally used until basically empty.
A rechargeable battery is rated for a number of charge/discharge cycles. By using extra full discharges of partially empty batteries, we possibly degrade the life of the batteries.
I hate to see a myth being propagated with the "refresh" concept. Any hard evidence out there?
To do a proper memory effect study is a very large project. First, a significant
number of cells need to be tested to avoid the effect of cell to cell differences.
All cells should have the same batch code (manufactured from the same batch of material at the same time).
Then they should be split in two groups and for several weeks one group should be on a
partial discharge/ charge cycle without refresh to induce a possible memory effect while
the other group is going through a discharge- refresh- charge cycle. All equipment needs
to be identical and it needs to be under temperature controlled environment. Each cell
needs to be identically mounted and ventilated to avoid temperature differences to effect the
test. At the end of that preconditioning period, both groups are evaluated for ability
to deliver a full discharge.
It is actually rather easy to test a D1 battery and get reasonable accuracy. First of all,
one must start with a fully charged battery, which sounds obvious, but to really get it
fully charged, it should be left on the charger for at least an hour or two after the green
light comes on. It will continue trickle charging afterwards. At the same time,
the battery will have time to cool off after the fast charge cycle.