Why? With the 2900s In almost ever test I've seen the Panasonics are always bested by almost every cell. And when it comes to vaping mAh they also rate poorly.
Here's a 3A test with a Panasonic 2900 (AW2900).
The Sanyo2600 is beating it in every single aspect, higher initial volts, less voltage drop and more vaping mAh.
In a single cell PV if we use 3.4V as our performance cut-off, the Pansonic's performance, done at ~1200mAh, is actually dismal compared to the Sanyo's ~2000mAh. And in no way is this test unique.
4.1V is actually pretty pathetic and far from optimal and if that's right off the charger after a rest, especially if the cell was not fully saturated it will drop even lower, it is probably only at about 80% capacity. I saw those $3 chargers you are using, they are especially prone to simply cutting off at voltage without finishing (fully saturating) the cell. Your 6 charger array is expensive, inefficient and actually looks dangerous. You are probably are only getting about ~280mA out of them, rather pathetic for anything except the smallest cell.
For folks who want to charge multiple cells this seems to be a decent choice.
Review: Trustfire TR003P4 Charger | BudgetLightForum.com
They can be found on eBay for less that $20.
