On the double-charger, I slide each metal (springed) battery platform (can't think of a better name...lol) down most of the way to leave alot of room to position the batts so they are completely lined up, centered, and not askew/crooked at the top within their slots. Then I slowly (and manually) move each metal platform up to the batt bottom (-) so it gently touches and finally locks it into position. Most times it hits it right on target where the n**ple (self-censor...lol) end (+) of the battery is in the correct spot at the top, sortof under the bump there.
It's so easy for the batts to slide around in there, especially at the top, causing it to miss where it needs to be to get a charge (and the light never turns to red). Part of the problem may be because this type of charger does multiple battery types. Am guessing some pretty thick
batteries could also go in there based on how big the slots are.