As a night photographer I’m a proponent of the philosophy of “carry a big battery” and you’ll never miss that shot. However I learned a hard lesson about my corral of batteries that I feel I must pass on before you too shriek in terror when you find your once reliable battery has met an untimely (and inconveniently timed) demise.
Lithium Batteries are Greatly Disturbed By Heat
This was the lesson I learned the hard way. I had a stable of five fully charged batteries ranging in size from 1800 milliamp hours all the way up to 8,000 milliamp hours. I kept them in a shaded part of my car through some summer days in the San Francisco Bay area. And that was how I learned that Lithium + Fully Charged + Heat = premature death. The two low capacity batteries previously allowed me two and a half hours worth of continuous night exposure. Now they each last about 12 and 15 minutes. The three HUGE batteries that could easily power my camera all night long for continuous exposures now have about the same life in them as my regular 2000 mA hr batteries – that is, about 1/3 as long as they used to last.
I learned why my brutish batteries became so feeble at Battery University. In a nutshell I discovered that storing batteries cool (less the 86 F) and at 40% charge is the most effective at prolonging their life. What I do now is keep all of my batteries in a separate pouch which I take with me into my office or home – even if I leave my camera equipment in the car.
I’d like to heed the 40% storage method – but not all of my chargers accurately tell the battery capacity. And worse, when I’m running out for a night of exposures, I usually don’t have an extra hour or two to fully charge my workhorses.
And yes, repeated discharge and recharge of those batteries will diminish their life, but NOT as fast as fully loaded batteries baking at a mild 90 degrees or more.