Canon SPEEDLITE 270EX II Mode D'emploi page 8

Note that certain AA/R6 lithium batteries may become extremely hot in rare cases
during usage. Due to safety reasons, do not use "AA/R6 lithium batteries".
Be sure to use a new set of two batteries of the same brand. When replacing the
batteries, replace both batteries at once.
Do not fire more than 20 continuous flashes in a short time.
If you fire more than 20 continuous flashes in a short time, the overheating prevention
function may be activated and make the recycling time about 8 to 20 sec. If this occurs,
allow a rest time of about 15 min. and the functioning of the flash will then return to
normal.
If you change the batteries after firing flashes continuously, be aware that the batteries
might be hot.
Using AA/R6 batteries other than the alkaline type may cause improper battery contact
due to the irregular shape of the battery contacts.
AA/HR6 Ni-MH batteries can also be used.
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