I would have gotten the lithium in a flash (no pun intended) but it specifically says not to use anything other than alkaline.I take the batteries out when I'm not using the flash. You may want to consider saving up for a rechargable battery for it- not rechargeable AA's though. If you need to stay with AA batteries for now then get the more expensive lithium batteries and make sure to remove them from the flash when it's not in use. My experience has been that all camera equipment eats regular batteries very quickly.
Canon Speedlight 430EX IIWhat flash do you have? I'm sure you have different options.
ok, just reread the manual and it says that they are fine...I guess I didn't see it earlier since it is at the very bottom of the page...