Ian, I've never carried the charger with me yet! I have four batteries but usually only carry 3 on two week trips. I usually camp and rarely stay in accommodation. There were times when I used film that I ran out and had to hike out to buy more - often finding little choice of film so I ended up traveling further by bus/train/thumb in order to buy the film I wanted.

I'm unlikely to ever be out for more than 3 weeks without supply and I'm happy to carry enough batteries for that period. In hot areas I would certainly now consider a solar charger. On the Arizona Trail, where I first used a digital camera (a 2.3mp compact) I found I could revive "dead" batteries simply by placing them on a dark surface in the sun!

Most of my batteries are 3rd party ones. Sometimes these seem better than those from the camera makers!

Thanks for the feedback Chris - very useful.

Quote:
"I found I could revive "dead" batteries simply by placing them on a dark surface in the sun!"

I've not heard of this before. When it's cold I often alternate between the battery in-camera, and one "recovering" in my pocket. I can get a lot more life out of a frozen battery by doing this, but I've never considered your dark surface method in more normal (or hot) temperatures. How much more life can you get? Enough to squeeze out a few last shots, or a considerable amount?

Ian, I usually carry a spare battery in a pocket when it's cold and swap it for the one in the camera when that one fades. On the Arizona Trail the batteries would last for twenty or thirty shots after being heated. They were hot to the touch after half an hour or so. These were AA batteries. I haven't tried it with Lithium-Ion batteries nor in Scottish temperatures rather than Arizona ones.

For every 10 degree C rise in temp chemical reactions tend to happen twice as fast. So flattish batteries might be persuaded to give a few more shots just by heating them to body temperature.

I'd avoid overheating them though. Generally high temperatures aren't good for batteries, resulting in a shorter lifespan. This is the reason slow charging is recommended rather than fast charging (where the option exists).

Of course, it might be felt that those few more shots are more important than the batteries, in which case it might be worth overheating them.


"Testing has shown that continuous exposure to 45°C will reduce the cycle life of a I-MH battery by 60 percent and as with all batteries, the self discharge rate doubles with each 10°C increase in temperature.

The conclusion is that elevated temperatures during storage or use seriously affect the battery life."

Thanks for that info John. In Arizona I was heating alkaline batteries so any harm that might have done didn't really matter as they'd ceased working anyway. Obviously more care is needed with rechargeable batteries (especially expensive Lithium ones). In temperatures of -35 degrees C I've found that the battery in my DSLR lasts for about 15 minutes while taking photographs! Swopping it with a spare from an inside pocket gives another 15 minutes. Once warmed up in my pocket and when the temperature has risen to -10 or above a battery will last for 100 shots or more before needing to be reheated.

The self discharge rate information is interesting. That suggests that in warm climates batteries should be kept cool. I wonder what the optimum storage temperature is for batteries? So far I've found batteries far more affected by the cold than the heat.

Li batteries are actualy quite tollerant. They can be stored anywhere between -20 and +60 degrees C. The ptimum is oft quoted as being around 15 degrees C. Its important not to store them for long periods when completely drained. The latter is perhaps the biggest danger for Li cells on long trips.

Useful link battery storage and performance

direct link to storage page

Thanks Dave. That's useful information.

A further note on reviving batteries. Last night I was camped up in the hills and taking photos at dusk when the battery in my Sigma DP1 compact died, the battery status showing red, which means "the power of the battery is empty". I had intended to change it this morning, having kept the spare battery warm overnight (the temperature fell to -8C inside the tent). However as the sun was shining in the tent I placed the camera, which is black, on an insulated foil bag and left it there for half an hour. The temperature in the sun was +10C. The camera then started and showed a low charge. I continued using it all day in sub zero temperatures and took 44 photos.

Until reading your posts Chris I wouldn't have thought about putting the camera/battery in the sun. I'd have tried removing the battery and keeping it in the sleeping bag overnight. My logic (it's all I have ;) ) tells me this would have had a similar effect in this particular situation.