Probably more significant is the fact that the Sanyo NC-MQNO6U is only a dual-channel charger. On top of that, it's a 'slow' charger, taking 10 hours to fully charge. Although there's some mention of being a 'smart' charger, Negative Delta V isn't reliable with low charge rates, so it's more likely the charger relies on a timer and temperature monitoring. This type of charger is not friendly to NiMH batteries, but cheap to make.
The Panasonic BQ-CC55 is a proper smart charger with 4 independent channels, although power supply limitations mean it takes twice as long for 4 batteries as 2. I would be favoring this charger for all the batteries, if possible. If you need to use the NC-MQNO6U, try to keep the batteries in pairs (label them) and don't mix them up.
You can crudely compare cells with a multimeter. You want each pair to have a similar voltage at full charge and when at least half discharged.
No, but here is the full specification.
What really caught my eye was the fact that this is a variable current charger! Although the average for two cells is 1.5A, the peak is 3.2A! I assume that after stabilization, the charger increases the current and monitors the battery temperature. When temperature reaches a certain point, the charger starts dropping the current, obviously to way below 1.5A.
It's always been conventional wisdom that NiMH should be charged with a constant current until negative delta V occurs. The Maha charger probably takes this to the point of obsession (yes, I have one).
I would love to get my hands on one of these to see it in action. Might be hard to measure the current on something that's effectively monitoring impedance though.
In order to fully change NiMH batteries they're going to get warm. There are some chargers that will thermally throttle the charging current at the end so they don't get as warm by monitoring the battery temperature, but that makes it harder to detect the -dV peak.