rhizo,
So....200ma vs 500ma....that's the question, and I am a nerd so I did quite a bit of research on it. I am going to try and sum a few things up, and I am bad at generalizing, but here it goes.
First some background, I don't know if you know how a charger detects when a battery is 100% full or not. But basically when the battery is charging the voltage will go up and up and up, until it is fully charged where it will have a negative voltage delta. At which point the charger should stop charging as soon as this happens, and go into trickle.
Second, it is important to note that C and ma are not directly correlated across different batteries. The C value is based on the ma and the capacity of the battery. I will explain my recommendations later (even though I am not qualified, nor do I have any reasons for you to listen to me).
Now why 500ma? It is because that with 200ma that negative delta may be very small. Because your charging so slow, the charger may struggle to sense this small negative change. And thus continue to charge, until failure (or overvoltage detection).
Apparently on further reading the BC-900 charger linked at the top has reports of melting down. Although I have heard conflicting reasons (some say it could not detect the voltage delta at 200ma with high capacity batteries, ie 2500mAh or higher, some seem to report the problem with using the 1000ma charge rate). And the BC-700 was introduced in the market as a temporary fix for the problem (which is why my charger can only charge at 700ma, and i did not even know the other model could do higher). The BC-900 should now be fixed of these problems. There is an additional safety feature which will cause it to stop charging at a particular voltage (i think i read it was like 1.55volts), because the charger assumes that at that point it has just missed the negative delta voltage.
(on a slightly seperate topic, it seems most cheap chargers avoid these problems by: having a low charge rate, so that the heat stays low...and then having a low over voltage cut off (even as low as 1.45 volts) so that it is safe to assume it misses the negative delta, but can remain safe....the end result is a battery with about 70 to 90% of it's possible charge, and wont last even close to the life as when used on a good charger)
More confusion:
As cells age, they need a higher charge rate to detect this negative delta. And additionally some have evidence to show that too slow of a charge rate may not even fully charge a cell (meaning the negative delta was detected too early somehow, i have no idea how this could happen).
So, a lot of long winded answers, and what did I personally decide? Well with the 2700mAh sanyo, should always be charged with 500ma or higher. With the lower capacity 2000mAh eneloop's 200 or 500ma is probably fine when they are newer, but you may not be getting the most of the battery, and as they age the risk of not detecting the negative voltage is higher.
So I plan to always use 500mAh on my AA's, and use the 200mAh on AAA's since their capacity is much lower. Based on what I read the 500 (and some even argue that is too low, and you should be staying closer to the industry recommendations of about 1000ma for a 2500mAh battery) is probably the safest bet. Less likely to overheat than 700 or 1000ma, and yet your more likely to get a good charge and detect the voltage drop.
Let me know if you have any questions, I feel like I understand this stuff decently enough, but I probably did a terrible job explaining it.
Oh, and anyone else that see's this thread in the future, check out this charger:
http://www.amazon.com/Maha-Powerex-...1?ie=UTF8&s=electronics&qid=1262642413&sr=8-1
That charger seems to have several benefits over the alpha charger. Including that on the charger/discharge cycle it pauses for one hour after the charge before it starts the discharge. This is the industry accepted procedure, vs the alpha which immediately starts to discharge. And in addition this charger seems to do some slightly different techniques once it detects a negative voltage delta (instead of going immediately into trickle, it drops the charge rate to 100mAh for a bit, then trickles, testing by a few forum users has shown that this produces a higher charged battery, no comments on safety, but I did not ear any complaints about this procedure).
