eh, I cannot resist responding to the question of chargers, charging rates, and NiMH cell temps at moment of charge complete detection.
I believe that SilverFox and others have several stickies on Ni-MH chargers, and some of those tests include the cell temp at termination. I recommend searching for an reading those reviews first - a lot of work went in to those reviews, for which the CPF Community is truly thankful for data, not opinions!
Having provided that disclaimer, I will proceed to give my opinion based on years of Ni-CD and NiMH cell charging. I understand the recommended theory about charging at some C or fractional C rate. However the same charge rate from different chargers also heats the cells differently because of very different charging algorithms. I am not aware of any modern charger that uses a straight DC charge current. They all have various pulsed charge algorithms with more precise or more coarse charge cut-off methods. FWIW, I have or had, 2x BC700, 3x BC900, 2x Maha 9000, various Maha chargers including the C800S or C801D, 5x Sony charger BCG-34xxx, Kodak, etc. etc. So I have had enough samples of most chargers to differentiate between a sample of one with a degrees of freedom of zero, or at least a couple copies to ensure that my experience was not an anomaly.
Frankly, I am surprised at the rather wide cell temp differences upon detection of charge completion assuming approximately the same charge rate, but using different chargers, to the extent I am able to control the charge rate.
It is understood that a very slow charge rate will not reliably detect the charge completion signal, usually a slight decline in cell voltage. The better chargers have a higher resolution to detect this change.
However, at some point, all chargers I have possessed have missed charge termination with new cells or cells that have been sitting for months if not years, even with the "recommended" charge rates for the cell capacity. New NiMH cells that have been formed at the factory cost more than the lower-cost cells with no forming. If you purchase the lower cost cells, expect to spend some time in forming the cell. Some cells require 10-20 cycles of what could be considered normal charging before they demonstrate a capacity even close to their rating. Hence the "forming charge" feature in the Maha 9000.
The BC-900 or BC-700 default to a 200ma rate for any cell. As Silverfox has amply explained, although the charger will terminate the charge on a 200ma rate, there may have been some overcharging before the completion signal was sensed. On the other hand, pushing 1000ma into each cell with 4 cells in the BC-900 charger will result in a high cell temp at charge completion. Even a 700ma charge rate in a BC-700/900 results in high cell temps - whether too high or not is an opinion. I did measure the temps with a thermocouple a few times with different charge rates and noted that the temp was below the cell manufacturers max rating. However from experience I know that using an electric/electronic device up to it's max rating nearly always means a shortened lifetime, batteries included. I personally prefer the 500ma charge rate with either the BC-900 or BC-700 chargers. And I do like the BC-700 charger because the power supply is smaller so it travels more compactly, and I would almost never use a charge rate above 700ma.
The Maha 9000 defaults to a 1000ma charge rate, but the charger is physically larger to space out the cells such that they do not heat each other, and the charging algorithm is different. In general, the Maha 9000 results in lower cell temps at charge termination for a similar charge rate.
The Maha C800S and C801D offer different charge rates, but also tend to result in lower temps at charge completion. The C801D was sent on a 1 year sailing trip, served well, and survived lightning strikes on the boat! The choice for the C801D was made because of the higher charge rate since they were using solar cells for the basic power source. IOW, use the solar cell power while the sun was shining rather than lose efficiency by charging the boats batteries to allow charging over a longer period of time. The C800S was later selected because of it's lower charge rate. Both went on the year sailing trip. Irrespective of posted comments as to what a proper charge rate for NiMH cells should be, Maha designed both chargers, and both chargers function quite nicely.
Also, there are some chargers identified in the Silverfox testing that excessively heat the cells. My family has traveled extensively in Europe. Both daughters have had melted cell sleeves and worse when using the C401FS on a 240VAC mains when set on a high rate charge. A slow charge setting did not seem to melt any sleeves. The point of the comment is not to complain about one charger or another - go read the tests from SilverFox!
Ref the recent posts about a charger/cell self-destruct in SE Asia. One of my engineer friends had a charger self-destruct in the US on 120VAC mains as well. As Silverfox posted in that thread, do not take any charging process for granted. Keep checking any charging process to ensure no surprises.
