Why? (in General)

"Didn't I say it's not polite to fight more than one battle at a time? You'll have to wait about 10 minutes now for fight to be reenabled.

(Multiple suspensions will result in longer penalties.) "

And I didn't even get a warning before I was suspended, now I will have to use my remaining 79BA without clan bonus.

If you click 'Fight' before the server has had a chance to send the warning page, your browser won't bother to download and display that warning page (as it concludes that you apparently wasn't interested in it, as you already clicked for another page).

The only way (apart from rare, real bugs on the server's side) to never be in more than 1 battle at a time is to always wait until your browser is completely done loading the page before going to the next one. Of course, this is slow. The trick is figuring out how much you can speed it up ;)
If you always wait after each click for your browser to display something, before clicking again, the warning should have been displayed. If you're just rapidly hitting enter, you may have skipped the warning.