How long do you leave them on the charger?
I put them on the charger at 9am and I take them off usually around 2pm.
But I have been known to leave them on until around 5pm sometimes.
NOTE: I charge them in a Liposack just in case.
One thing to note is that when I take them off the charger early, they feel a little warm.
But if I leave them on for a long time, they are cool to the touch when I take them off the charger.
How long do the batteries last you?
I don't know, I'm still using the two that I got 7 months ago.
But keep in mind I am a pretty light vaper, using about 1ml or less per day.
Maybe my charger has a lower cutoff for safety reasons.
It sounds like it to me, because I think mine is doing what it is supposed to do.
Check out this link from Vaping Zone...
Efest 007 4.8v Ni-MH dual charger
EFEST 007 4.8v Ni-MH dual charger
Detailed Product Description
1. it can charge 2pcs 5V batteries
2. it fits to your 5V E-cigs mod
3. the sizes is same with 18650 and 17670 batteries
Charge 2 X 4.8V - 5.6V Ni-MH battery Not for use
with 3.0V -3.7V battery connect the power cord
to the charger,and insert the plug into the power
outlet, Recharging starts automatically and the
charge lamp turns red, when the battery is fully
recharged , the full-charge lamp will trun green.
So this is same charger you have, but it seems to indicate the batteries charge up to 5.6 volts, which mine do.
In fact, often right when I pull them off the charger they are even up over 5.7 volts.
The highest I've ever seen them get is 5.78 volts.