max said:
NiMH batteries and chargers are interchangeable. Any NiMH batteries will do fine in either charger.
It would seem so for the most part. However, there are some exceptions to this general rule. We have firm evidence that it is not be the case for all situations since some chargers are not as responsive to the needs of the NiMH chemistry as others. At this point, the overall consensus internally is that nearly all NiMH chargers will work with nearly all NiMH batteries, but that poorly built fast chargers are likely to diminish the overall longevity/life of the battery (the number of complete charge cycles).
There are two main issues associated with battery charger quality: 1) the manner in which energy is delivered to the battery, and 2) the method used to determine when charging has been completed. In regards to charge energy delivery, there are two approaches: "slow charging" and "fast charging". In slow charging, energy is delivered at a low constant rate that does not require charge endpoint determination. This is the type of charger we bundle with the Box. They are not the "best" chargers, but they are reliable, simple, and safe.
Fast chargers are much more complex (and thus more expensive), since they deliver energy at a much greater rate than the battery can sustainably withstand. For a fast charger to be "good", it must perform two tasks: 1) it must deliver charge current without surges, ripples, or spikes, and 2) it must reliably determine when the battery is full and shutoff the charge current. Failure in achieving either of these aspects will definitely shorten NiMH battery life (the number of recharge cycles and the max energy that can be stored per cycle). Specifically, the current delivered must be matched against the battery capacity. Also, if there are surges, ripples, or spikes, the battery discharge characteristics can be adversely affected. This in turn can result in a Box running either way too hot or way too cold, depending on the type of battery damage sustained. Furthermore, if the charge endpoint is not determined correctly, the battery can be overcharged, resulting it its getting very hot (too hot to touch) which will also permanently damage the battery.
Unfortunately for fast charger manufacturers, determining when a NiMH battery is "full" is far from easy. The battery itself provides little indication of its internal state. There are three approaches generally taken: 1) use a timer to cut off current after a given interval, 2) to look for a specific sequence of battery voltage changes, and 3) to check the battery temperature and stop charging when the battery is hot. Each of these approaches has significant problems and is likely to fail if used exclusively. A good charger will need to test for at least two, if not all three, of these conditions to function reliably. It is in this respect that good chargers really stand out from their cheaper cousins -- they preserve battery life by not accidentally over-charging the battery. Many fast chargers on the market simply do not test for charge endpoint conditions very well or very reliably.
All of the above is generally accepted 'fact' -- now for some 'opinion': It has been my experience that Radio Shack (Tandy corp) generally cuts corners whenever possible in their product designs and their chargers are no exception. I have on hand one of their 15 minute fast chargers which has been made
specifically incompatible with other HiMH batteries via the use of hidden ID circuitry in the RS stock batteries (other non-RS batteries charge in slow mode only). While their newer fast chargers may not have this built-in limitation, they still have issues with charge current regulation and endpoint determination. I have some of our stock batteries (shipped back to us from a customer using a RS charger) which were definitely and identifiably damaged by a RS charger. While it may not be the case that
all of the RS chargers will do this, it is known that at least
some of them will. As such, I simply cannot recommend that people use RS chargers with our batteries. If people are looking for a good fast charger which we know to be reliable as an alternative to the shipped slow charger, we recommend using the Energizer 15-minute charger with our stock batteries -- this is the best overall all-around combination we can suggest for the needs of 99% of our customers. (Note -- the Energizer batteries themselves are not nearly as good -- take it or leave it).
Finally, for the record, I should point out that we (Magic-flight) do not make the slow chargers that we bundle with the Box, nor do we have any agreements (formal or implied) with any charger manufacturers. We gain no benefit from our recommendations or advice in this respect -- we have absolutely zero association with Energizer corp. Also, as there are hundreds of different chargers and batteries (with millions of possible test configurations), we have NOT tested all batteries and all chargers. Our recommendations are based on best available knowledge to date. If someone on this forum has more, or more accurate, information, they are welcomed to bring it forward.
Best,
-- Magic-flight
I'll save those 2 batteries (which arrived charged) for tonight. Now I just need a quick charger and extra batteries. It's amazingly small, the pictures do it no justice. a very nice looking piece. 
