I don't have and have never used a Sanyo 15min charger but I recently bought 4 eneloop batteries. They were fully charged out of the packaging - I tested the voltage and got 1.31V.
I then proceeded to test it by plonking it into my PD7X CompactDrive and repeatedly copying a fully loaded 2GB CF. I managed to do this 13 times before I ran out of juice. This means I copied 26GB worth of files (all RAW).
Finally, I used my LaCrosse charger to recharge it using refresh mode. The capacity that I got was 2.11mAh for 2 cells, 2.06mAh for 1 cell and 2.12mAh for 1 cell. Note that the rated capacity is 2mAh.
Overall, I'm pretty happy with it so far. It's nice to be able to use Ni-MH batteries straight out of the packing without having to charge it.
I guess it should be really that fast but you will probably not get a 100% charge after 15mins. Maybe only 80% or 90%. Many fast chargers will then reduce the charging current to a low value to continue charging. This is called trickle charge. I suppose this charger is no different.
However, note that fast charging a battery will cause it to be very hot (and I mean VERY HOT). This is not good for the battery in the long run. When getting a fast charger, be sure that there is a safety cut-off which comes into play when the heat reaches a certain temperature.
For me, which battery to get depends a lot on how I will be using it. That is to say, will I need more juice over a shorter period of time like not more than a few days? Or do I need it to still have power after a long period like a few weeks? Or do I store the batteries fully charged up and only use it after a long period?
The only battery that is able to hold its charge for long periods of time is the Sanyo eneloop. Even after one year, it still retains 85% of its charge. The downside, for the moment at least, is that it comes in 2000 mAh capacity only.
All other Ni-MH batteries cannot hold their charge for more than a matter of weeks. But then there are larger capacity versions, up to 2800 mAh.
Both the Powerex and Sanyo batteries are good. Some say the Powerex is better but others beg to differ. I don't think the difference is a lot, if any.
Some points to consider when choosing a battery:
What is the largest capacity available?
How long can the battery hold its charge?
How many times can the battery be charged before it loses too much capacity? Note that, generally, the larger capacity, the lesser the number of times the battery can be recharged.
For use in an external flash to be used for shoots like events, I will use larger capacity batteries. For use in p & s cameras, I will choose the Sanyo eneloop as I would want to be able to plonk in the batteries and be able to use the camera straight away anytime without having to recharge the batteries.
i'm using the 15min charger, works well, cuts off at 15mins and there's a fan below the charger to keep the batteries cool during the charge. the batteries are not any hotter than those on the conventional sanyo chargers.