I accidentally charged a phantom 2 battery with the phantom 3 charger. I'm assuming it's safe otherwise the plug wouldn't have fit into the battery? Anyone know to put my mind at rest. Could I have damaged the battery in any way and is it safe to use?

Which watt charger?  I doubt you did any damage if it was only once and I wouldn't worry.  I have done the same thing and have not had a problem.  The plugs are the same, it is the wattage/trickle current that is different.

Should be fine. The Intelligent battery has some smarts built in. Not recommended, but I've heard pilots hook up Car batteries directly into the battery and have had success.
And analogically speaking,  putting a smaller feet into a larger shoe wont damage the shoe. However, it was the other way around - charging a P2 with a P3 charger MAYBE a different story.

The 57 watt phantom 3 advance charger. I noticed the phantom 3 charger output 12.6v ar 4.0a while the phantom 3 outputs 17.4v at 3.3a. I noticed the phantom 2 charger also fits into the phantom 3 battery.. I wonder why dji made it so they can be swapped accidentally. Basically I charged my phantom 3 battery at a higher voltage but lower amp..is that bad?

Sorry I meant I charged

My phantom 2 battery at a higher voltage but lower amp