I wrote a thread the other day explaining a problem with my vtc4s. I used them for about a month, then started noticing they were not holding charge. after about 15 minutes of use they would be back to 1/3 life (as shown by the light indicators on my nitecore i4 charger). I bought a couple efest batteries as replacements the other day, and they were working great. now only a few days later, I am noticing the same thing happening to them that happened to my sonys. what could be causing this?!? I have been leaving them on the charger overnight, could this do something?? I also noticed when I first bought the efests the charge time was pretty long, now im seeing they charge faster... im just looking for someone with advanced battery knowledge to help me figure this out