Re: How much maximum BTC can be sent in a single transaction?
21,000,000.. max
This is the only correct answer that i see. 
haha, that is actually not technically correct
first of all is the fact that we can never mine all the 21 million coins because reward is halved so it will never actually reach zero.
secondly is taking all the lost coins into consideration, a lot are burned by being sent to burn addresses, a lot are lost because someone forgot the private keys.
third if we ignore all the second step, there is 1 satoshi from missing from all the mining rewards thanks to a miner who intentionally got underpaid 1 satoshi less as an honor to satoshi missing. so even if all the coins are mined the total number will be 21 million minus 1 satoshi.
But you still forgot something important. We can't send the max amount because there will no transaction fee will left for the transaction. Hahaha. But honeslty speaking. There is no such maximum amount for BTC to send right now because it is impossible to gather all BTC in one wallet.