Flash battery question

[Guest #12]

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...may be a dumb question, but when do you discard batteries--at a certain % of the nominal voltage? I found out the hard way, 95% was not enough to keep the flash (SF24) from stalling. Is there such a thing as a load test for little batteries, or do you just check the voltage?

[giordano]

Lithium primary (non-rechargeable) cells like the 123 series recommended for the SF24 have a rather flat discharge curve, meaning that the voltage doesn't change much between new and almost-fully-discharged, so neither a voltmeter nor a load test will tell you very much before it's too late.

 

The best load test for a flashgun is to fire two or three shots on full power in rapid succession and then measure how long it takes to recycle compared to the same test with new batteries. With alkaline cells, a doubling of the full power recycling time means they're near the end of life. With lithium primary cells I guess it's more like a 25% increase.

 

But the only safe course is to start any long important session with fresh batteries in the flashgun and spares in your pocket.

[Guest #12]

Thanks for the detailed answers.

 

I usually have extra batteries and an extra speedlight; just not yesterday.

[jaapv]

I found out the hard way that the SF24D does not accept rechargable 123 cells.