Ok so IMO the last chapter showed that Edo tensai have unlimited chakra not Infinite Chakra
I just wanted to clear up the difference between the two
So Infinity is infinity, you cant subtract from, add to it...... multiply it.....or do anything; infinity/2 is infinity......
So here http://narutobase.net/manga/Naruto/656/4
we see hashi says you now do not have enough Chakra to use preta path
So as i have established you cannot subtract from infinity, then it is determined the edo tensai chakra is unlimited which implys that their chakra regenerates when it hits zero or when they reanimate from being wounded...
Madara's chakra was prolly close to 0 and was trying to regenerate but the wood dragon just continuously sucked it out
(if you knew this dont bother posting lol)