if I have 2 Lipo batteries at 20C discharge each... if both of them are 2200mah will I end up with a 4400mah battery when I connect them parallel?

That is the theory.

In theory yes, but you may have balance problems between the two cells.

Parallel: V remains - Total A adds

Series: V adds - Total A remains

cool... what happens when the discharge ranges vary? say 15C with 20C...

It can get messy with one battery possibly acting as a load on the other battery. Best to NEVER mix capacities in parallel.

gotta remember that electricity is very lazy.......the higher capacity battery could see a path to ground through the lower capacity battery.....that equals a short and smoke.......

And always remember all electronics run on smoke. Once you let it out you can't put it back in again.

Hogflyer

Basically you will end up with a 4400mAh battery. and voltage will stay the sam eif connecte din parallel. Another benefit of a parallel circuit is lower overall resistance.

As for putting different capacity bateries in parallel, I have done it with NiCad and NiMH receiver packs. I was told I'd have all sorts of problems but there were none whatsoever. In fact, after flying the plane I could recharge each battery and found them to both always to be drained in equal percentages. For instance, let's say I had a 1000mAh and 2000mAh NiMh in parallel. After a day at the field the both would take roughly 40% to recharge. In other words the 1000mAh pack would take 400mAh to recharge and the 2000mAh would take 800mAh to recharge. These numbers aren't exactly what I got of course, I just used them for demonstration since they are simple. I checked this on numerous occasions and always found the batteries to be drained in equal percentages. Now, the batteries were the same cell configuration and from the same manufacturer. Both always fully charged using the same charger.

I didn't need any diodes, special circuit boards or anything else. What would have happened if there was a major cell failure in one pack? Not sure but I fifgure I'd have issues if that happened regardless.

This was with Nicad and NimH now... Lipo's may or may not be the same. I don't know enough about them to say either way.

When it comes to mixing c-ratings in a parallel battery circuit, I have no idea on that either.

Yes, however if the capacities are identical you should be fine. It is advisable to use matched ( same manufacturer ) packs.

I normally use identical packs and I've run parallel 14.8v 5000mAh packs to obtain 14.8v 10000mAh equivalents, parallel 2200mAh 11v, parallel 5C 3750 packs, etc.

I've never had a problem.

I use a computer controlled ( Team Checkpoint ) charger with a balancer, to make sure that the packs are charged to the same level as well.