While a number of manufacturers have stated that the minimum charge rate be greater than 0.5C to generate a strong enough signal for chargers to detect and stop charge, there was a point raised that it should be a "fixed" number or fixed current level...especially for smaller capacities, see below:
I have another charger that shows exactly the same pattern with vibrant AAA eneloop batteries where the rate is 0.14C (175mA) and that batteries do not terminate, yet, the AA batteries at the same 0.14C rate do terminate ???
When I alter the AAA charge to about 280mA (increase of 170 mA), the termination is very reliable.
Based upon these empirical tests on a few chargers, I would suggest that a minimum current of 280mA be used for both AA and AAA batteries if smart termination is to be used. Out of curiosity, I want how low it can go ?
Owners of programmable charge rate charges (eg. Maha C9000 or La Crosse BC-900) could easily verify the claim and perhaps find a lower limit by using the this current with a 10 minute temination test. A lot of La Crosse owners already know that default 200mA does not work for a lot users. Early Maha C9000 units were set to a 1000 mA default.All things being equal, the smaller AAA battery should be able to terminate more reliably at a lower current level but I believe it does scale (with capacity) from the AA number.
Last, as the charge current drops, I believe the termination algorithm has be that much better (than at higher currents). The units that terminate with the lowest currents should be the most tolerant of less than vibrant batteries.