As seen on crowdfunding site Indiegogo — Tenavolts has created very impressive 2,775 mWh rechargeable lithium AA batteries. Compared to the usual rechargeable NiMH batteries, they claim that their lithium batteries sustain 1.5V for longer, charge faster, and retain more capacity after repeated charge cycles.
These seem perfect for use in Speedlites and other situations where voltage droop can impact flash cycle time. They list some real-world tests vs. eneloop pro batteries that are convincing.
The only downside appears to be the price, at $32 + S&H for 4 AA plus charger or $59 + S&H for two sets, this costs more than your usual premium rechargeable NiMH batteries. However, if the performance is as claimed, these could be easily worth the price! The crowdfunding offer is a “super early bird” savings over their expected retail price.
Check out their campaign at Indiegogo, which only runs until the end of the week.