I go through many hundreds of batteries per year- it's crazy! Just about everything in my studio is electronic or uses electronic accessories. It seems to get worse every year. Some of the equipment uses ordinary disposable batteries, othere use rechargeables and some have those newfangled super-high tech batteries that one needs a degree in electronic engineering to understand.

So... of course I do have my handy battery tester that can test most ordinary alkaline batteries etc. of a variety of voltages under load and the load is adjustable as to the usage- not bad for a no-name meter that I purchased 20 years ago from my battery supplier. It works well and gives me a pretty good idea of battery condition and what I coud expect from any given battery. I did, at one time "calibrate" it to a more precise voltmeter so I have some idea of the actual voltage drops as the regular batteries diminish and expire.

As for rechargeable batteries- I have every manner of those things in my flash gear. Some are Nicads, othere are sealed lead-acid batteries. I have all kinds of chargers to accommodate each type of battery. So...at one time I wanted to monitor battery charging rates with a milliampere meter in series with the charger to insure proper charging rates, maxamize flashes per charge and extend eventual life- longevity of the batteries. With 10 portable units, a bunch of speedlights and a drawer full of radio slaves, exposure meters and camera batteries this started to become a kinda full-time job. Our dead battery bucket was filling up at an alarming rate.

Most importantly, I did no want batteries to unceremoniously drop dead right in the midst of an important job- and usually at the most inopportune times. So here are my preventative remedies.

I like the battery tester you show. That is exactly what I was looking for! Of course several people have brought up the fact that different chemistries in battery manufacture will make a difference in how the batteries test. I still would like to get my hands on the kind you show, but also a digital one as well. Someone said they feel a battery that tests around 1.565 and above is good to go, so between the two meters I can be pretty safe in what to use and what to discard.

Thanks again all who responded. I received some very good information about batteries as well as chargers.

With speedlights I just keep lots of spare batteries and on long jobs like weddings and events, I change them long before the are likely to die. On some of my units I created a 4 AA cell substitution pack made of wooden dowels, metal wood screws and wire. I place this device in the battery compartment of the speedlights and wire it to a home-made belt pack containing a sealed lead acid battery, 1- 6 volt battery, costing about 30 bucks, will deliver hundreds of full power flashes per charge and last about 2 to 3 years in continuous operation. No more tons of AA cells on long gigs. I have automatic chargers for theses batteries that automatically go to trickle charge when the battery is fully charged. Since theses batteries do drop a bit of voltage as they discharge, the recycling times slows down a bit and I know when it's time to change the pack- they won't drop dead without warning.

In my Lumadyne (bigger more powerful portables) I have replaced all of the expensive Nicads with theses sealed lead acid batteries of the same voltage and ampere/hour rating as the originals. A replacement set of originals costs about $200. the substitutes set me me back $40 each for a 12 volt battery.

Even with all my previous fussing and testing and my converted units, I have found by experience that even the best batteries, the best chargers and the best electronic gear can get "funny" and malfunction so the best bet is to carry plenty of spares. Used to be if you camera battery died the only thing that would go down was the metering system. Even film camera with electronic shutters had one mechanical speed that could get you through a job- not anymore. If the battery fails the entire camera goes down with it so the only solution on long jobs is plenty of backup.

Used to call the battery industry the "battery industry"- not anymore it's now ENERGY STORAGE! I get newsletters with all kids of specification and news of the advancements MORE SOPHISTICATED! Truly enough, there are some great inventions, innovations advancements and incredible minaturizations. Sometimes, however, the more sophisticated and complex things get, the more problematic they become. I have no time to run an electronics lab in my studio so I stick to simple batteries, lots of spares, reliable chargers and my beaten up old battery tester. I hate the smell of burning phenolic and overheated batteries so I try to keep the gear in good repair.

Our dead battery bucket goes to a safe disposal site every two months. Maybe we shoud have a ceremony!

See pictures of the meter and my battery conversion thing.

I test alkaline cells by measuring the voltage. If they are up around 1.52-1.53v then they are probably okay. If down to 1.49 then out they go. Voltages like 1.506 usually means they have probably been used a bit and not worth trusting. In this case they get relegated to use in torches.
Rechargeable batteries are charged, placed in series with some sort of load, and voltage across the load measured until the battery voltage drops depending on chemistry to a certain minimum value. From this you can calculate the average mA draw and compare it with the rated value of the cell. Do this up to 3-5 times to get an average. If the average is reasonable consistent and isn't too far from capacity then cell is probably okay. Worth repeating after a week to make sure the cell has held charge for a while. This is how you can tell whether a cell (lithium anyway) is either at its rated capacity of say 3000maH, or as often happens with some Chinese sourced (read manufactured) cells where the capacity might only turn out to be 1200maH. If you are handy with your hands you can make up a holder to fit camera batteries into for testing. Any battery not close to the rated capacity should be replaced.

I agree 100% especially in an application like 4 cells in series in a Flash if there is one weak cell ( not fully charged ) using it with 3 good cells will or at least could permanently damage it so that successful recharge will be impossible. So charge and use cells in matched sets. If you have Ni-MH cells be sure your charger is rated to charge them. Ni-cad cells can accept overcharging without damage but NI-MH can not, and the mechanism that the charger uses to detect full charge is different. So again be sure your charger is designed for Ni-MH if that's what your using.
Regarding using an external battery for your flash...is there sufficient frustration, and time wasted with changing and charging batteries that there is interest in the photography world for an external pocket or belt worn battery pack that can last thru 1000 s of flash cycles? I'm thinking of something with li-ion cells and electronics to supply a safe current limited and correct voltage for many thousands of cycles without re-charge.

Right now the Flashpoiht (Adorama) or Bolt (B&H) -- same unit, battery pack can be purchased for around 100.00. I purchased one of these units last year to use with a Flashpoint 360 flash. I have used this for several shoots and have not come close to draining the battery. In fact there are 5 leds on the top and I have not taken it down past two of them even when shooting around 500 shots one evening. I am so impressed with the battery and flash unit both that I bought another this year. The battery can be used either with the Flashpoint units or with Nikon, Canon units.

I have several battery testers: Micronta, Eveready, Sunbeam, Sears, etc. What I want though is one that will test the battery under a load. I hate it when I go through a pile of batteries, bag the ones that test totally charged and then try to use them in a flash unit or CD player to find they will only last for 15 min. or with flash, only about 25 - 40 shots! I guess I could add a resistor between the battery and tester but would anyone know what the average resistance would be for a flash unit using 4 AA batteries?