Thanks for the reply! I am afraid the first problem was my fault, I was using almost depleted batteries.
For the second problem, I did 2 tests. I got new Energizer rechargeable NiMH batteries with indicated capacity of 2450mAh. For the first test, I configured the batteries in parallel with diodes as shown below.
I set it to charge my girlfriend’s old Galaxy S with an empty batteries. The indicated capacity was 1500mAh. It managed to charge it up to about 70% in more than 2 hours. I also noticed that both the circuit and the batteries were getting very hot.
For the next test I put them in series was has been suggested. Again I started charging the Galaxy S (I drain its battery to 0% first). This time to my surprise, the whole battery was charged within an hour! I connected to another phone after that, and there was still some juice left! And also the whole thing was much less hotter. So indeed, your suggestion to put everything in series is a good one.
Above is the schematic of my series configuration. I added a switch to alternate between 3 or 4 cells, giving me the flexibility of using either the 1.2V rechargeable, or the 1.5V non-rechargeable.
And that a picture of my build. OK that all i have to say for now, thanks a lot for an amazing kit! really enjoyed it!