Hmm, the rechargeables at 1.26V weren't as fresh as I had thought. I fully charged a set of four and they worked out to 1.39V each. 5.04V I would have trusted enough, but I'm wary of 5.56V. It's not not as if a high current load will always be plugged in, and it wouldn't draw such high current when it's charge gets full too. So... the 4 rechargeable AA idea is out the window I think unless I want to throw in a 5V regulator that would waste power.
Alright, I just tried with two fresh rechargable AAs, each starting at 1.39V, totaling to 2.78V. My phone is at 22% power. The current draw from the batteries is 2.10A (Wow!), and their combined voltage is holding at 2.47V (A drop of only 0.3V, not bad for 2.10A!). The output from the MintyBoost is unfortunately not 5V, more like 4.87V.
The low output voltage despite input remaining strong, plus the 5.2W draw on the batteries, would indicate to me that most likely my device is trying to draw notably more than 500mA. Either that or I'm getting 50% efficiency and the MintyBoost voltage is being sub-par for a different reason, but I suspect it's the device trying to draw more than 500mA.
Performance after 10 minutes is:
- Device battery is at 28% (6% increase, out of a 1500mAh battery in the device)
- Means roughly a 540mA charge rate for it's battery assuming the 6% is accurate, and of course it's drawing more than that from USB considering the device is still on while charging.
- AAs down to 2.33V with 2.20A current. AAs measure at 2.59V when removed.
- MintyBoost output at 4.76V
At this point I really do wish I had a sacrificial usb extension to use for measuring usb current, haha.
After 1 hour of charging:
- Device battery is at 48% (26% increase). So an average charge rate of 390mA for the device battery over the course of an hour, assuming the 26% is accurate. USB current still unknown of course.
- AAs down to 1.64V total with 1.38A current being drawn. AAs measure at 2.38V when removed.
- The internal resistance of the rechargeable AAs went up significantly as they got low.
- MintyBoost output at 4.39V
So in conclusion... I don't know how much current the Samsung Galaxy S tries to draw, but seems evident that it's more than 500mA. I really should measure the actual USB current some time.