So I have learned that all batteries have an internal resistance which will limit the current that it can output, so that you can't discharge a huge battery in a split second because of that internal resistance. But what I am wondering is, at what point is it dangerous to draw too much current on lithium ion batteries. I took an 3.7V iPhone battery out (1900 mAh) and found the internal resistance to be very low through a couple tests, around 0.2 ohms or something. Later, I attached the leads to a very low ohm resistor and measured the current (like 0.1 ohms, barely anything). I actually maxed out the current on my ammeter, which is 10 amps, so I went over that mark. Hopefully I didn't mess up my meter, but I removed it quickly. The resistor also burnt out, but basically this tells me, I can pull a TON of current from this tiny little battery when it's not hooked to all the circuitry in the phone. Normally, it would be limited to only allow 500mA or something of the like. I am wondering, is there a good rule of thumb that will tell me what current is unsafe to draw off a lithium ion battery? I would think at some point, if I shorted the battery out for more than a few seconds, the internal resistance in the battery would get very hot and destroy, explode or catch the battery on fire. I just want to be safe here. I am not into short circuiting batteries, but I want to know how much current I can safely draw off of a lithium ion battery without causing it damage.