It's 4 channel. I was thinking how safe is it to use a bit of metal to charge a 16340 when the charge accommodates a minimum cell length of 50 mm. is the charger going to be too hard on the smaller battery?
In some cases, using a spacer to charge a smaller battery is not advisable, it all depends on the charge rate of the charger, and the cells being used.
Lets say for example, your charger runs at 400mA, then you can charge li-ion cells up to ~400mAH capacity pretty safely, but t would not be advisable to use a spacer to install a 250mAH 10440 size li-ion cell as it would charge too fast for that cell type.....
In your example above, you appear to have a pair of AWs IMR16340 cells in the charger. The IMR cells are a different chemistry than ordinary RCR123s, they can handle charge rates much faster than most consumer "bay" style li-ion chargers can provide, so in your case, here, there is nothing unsafe going on