RE: Barrel connectors- What's the current rating?
If the connectors are properly installed, my opinion is that heating up of the pack indicates that you're drawing a lot of current, perhaps more than it's capacity. Some heating is normal as long as it's not beyond the manufacturer's recommendation.
The "contacts" article I was looking for in Post #2 was actually on FlyRC, March 2004, page 46. They talk about Gold Bullet" connectors on Page 48 being rated at 70A. I assume those are the 4.0mm contacts (though they don't mention by name). I am interpolating their article to read that a 3.5mm contact is good for about 40A. But, that's just my own interpolation.
I should also mention this. I've been in the connector industry for many, many years. It doesn't matter whether you solder or crimp (flamers, hold off and read on before you push those buttons). A properly crimped contact is just as good as a properly soldered contact. Notice that I used the word "properly" twice. The problem is, when making up crimped connectors, many fliers mash the crimp barrels with pliers or something that is 'sorta close'. That just ain't gonna work. You have to use the crimp tool specifically made for that contact or you can just forget about it. Properly designed crimp tools are very expensive.
The same can be said for an improperly soldered connector. Trying to glob solder onto dirty wires or wire barrels results in cold solder joints that also work poorly, and then the flier blames the batteries, motor, esc. Again, refer to the "F" word in the paragraph above.
Anything less than a properly crimped or soldered connector is just wishful thinking. Wishful thinking doesn't let enough electrons pass through.
In short, one should use a proper crimp tool or the proper heat (i.e., not too high, not too low) when soldering. Overheating a contact can cause the contact leafs to lose their 'springiness' and not make sufficient contact. Overheating of the connector is a result.
I don't think that a poor connector joint will overheat a battery. The contacts should get no warmer than the surrounding wiring going in and out of them.
There you go, you asked me the time and I told you how to build a watch. I'm not saying that you fall into this category, it was just my way of mentioning some things...
Bob