Canon just told photographers to stop using lithium batteries in their Speedlites. This isn't a casual suggestion. The camera maker published a formal Service Notice this week, flagging lithium and lithium-ion cells as unsafe in its flash units, battery packs, and macro twin lights. The move caught the photography community off guard, raising the question of why this became a problem suddenly.
Lithium batteries pack more power into smaller packages than alkaline alternatives, which makes them appealing for portable flash gear. But that concentrated energy creates real risks. In flash systems, the rapid discharge cycles required to power recycling and firing can generate excessive heat in lithium cells. Thermal runaway becomes a genuine hazard, especially in compact enclosures where ventilation is limited.
The timing matters. Canon's warning suggests either incidents have occurred or testing revealed vulnerabilities that weren't previously documented. Other manufacturers likely use similar circuitry, which means Nikon and Sony shooters should probably check their own documentation rather than assume they're in the clear.
For photographers already carrying lithium AAs in their bags, the solution is straightforward. Switch back to alkaline batteries or invest in rechargeable NiMH cells like Eneloop. It's a minor inconvenience against the possibility of a battery failing catastrophically in your hand or bag. Sometimes the old tech works better for a reason.