As comparison examples of capacity, the Nikon manuals give these numbers for the Minimum Number of flashes, for a full power shot every 30 seconds (every 120 seconds for lithiums), from freshly charged or new batteries.
Nikon Minimum Number Of Flashes, full power flash, with fresh AA batteries
| Examples / | SB-900
page F-21 | SB-800
page 19 | SB-700
page H-27 | SB-600
page 19 | SB-400
(two cells) |
| Alkaline | 110 shots | 130 shots | 160 shots | 200 shots | 140 shots |
| NiMH 2000mah | 165 shots | 150 shots | 230 shots | 220 shots | |
| NiMH 2600mah | 190 shots | | 260 shots | | 210 shots |
| Lithium | 230 shots | 170 shots | 330 shots | 400 shots | 250 shots |
Alkaline AA batteries are available everywhere. Flashes need high battery current, and alkalines have the lowest capacity of these types. Alkalines cannot match the rechargeables, but alkalines do greatly better in speedlight flashes than do regular dry cells (non-alkaline, which are the poorest choice, regular dry cells will be dead very quickly.) Alkaline recycle speed is slower than NiMH rechargeables. but faster than Lithiums (previously true, but new lithiums are more equal today). Shelf life is said to be 7 years, so these are good as backup spares in the camera bag, for just in case. Alkalines are NOT rechargeable of course.
NiMH rechargeable AA batteries. Fastest recycle, because of lower internal resistance. These can be recharged hundreds of times, basically for free, however a good charger is required. Maha Powerex chargers
are a fine brand - most of their models charge each battery individually (with individual cell Status reporting, a separate status LED or LCD for each battery slot), (not required - cheaper chargers work too, in their way - but an old NiCd charger probably is a problem.) Individual cell charging is a big plus, not only because we can charge only one battery, but mainly because each battery is optimally charged individually - it gets whatever it needs itself, independent of the state of another battery. NiMH rechargeables are very popular with active speedlight users.
However, there are *TWO* types of NiMH rechargeable batteries today:
Regular NiMH cells - These self discharge sitting on the shelf, and will be near dead in a month or two, used or not. So these really must be recharged soon before any serious use. These regular type would be worst choice in something like a clock, or in the camera bag as backup spares (pointless where long life is needed), but they do work great and fast in flashes, if recharged recently, like today, or at least this week.
Newer type NiMH - which may be called PreCharged or Low Self Discharge, but they definitely should say something about a long storage time. Sanyo Eneloops are the classic leader, but there are several good brands now, licensed from Sanyo - these are the way to go today. One difference is that these have slightly less capacity than the regular type (2000 mah vs perhaps 2700 mah), so the regular NiMH might be bigger for a big shoot tomorrow - but after a week or so, the Eneloops will win. Because, the really big deal is that these hold their charge a very long time. Sanyo Eneloops say 75% capacity will remain after three years (unused), so these could be backup batteries too (still probably always good to rotate your backup batteries now and then.) If you want them to still be charged after a month or two, this choice is necessary. This long storage time is a huge plus if you only take a few flash pictures a week, these are still good to go after months. The packaging says you can use these right out of the package without charging first, because they don't lose their charge on the shelf. However, it won't hurt to charge them first, as the factory does not fully charge them. Using Eneloops, my SB-800 recycle time is reduced slightly, to 2.9 seconds.
Wikipedia says "eneloop is a brand developed by Sanyo encompassing rechargeable batteries and associated devices, introduced to the market in November 2005. The batteries are low self-discharge NiMH, which lose their charge slower than previous NiMH batteries; 10% in the first year compared to about 20% on the first day and 1-4% on every successive day. eneloop batteries are sold pre-charged and can be used immediately, while regular NiMH batteries lose their charge so fast that this isn't feasible."
Panasonic has bought control of Sanyo, and is replacing most Sanyo names with Panasonic.
FYI, the Eneloop info site and data sheets.
Lithium AA batteries These work well, with some advantages, except they will recycle more slowly (after every flash shot) than any of the others. Energizer Lithium AA batteries can provide more flashes than the others, if given enough time. Much better life than alkalines at high current loads (flash units), and much better than any in extreme cold temperatures. Shelf life and date stamp is 15 years. A bit more pricey, but better in most ways except recycle time. Even the weight is lighter. But these lithium cells contain protection to limit the maximum current for safety reasons. This means that flash recycle times are longer, which is a biggie when you don't want to wait for the next shot. Eneloop NiMH rechargeables remain my own choice for my flash use. AA size lithium is NOT rechargeable. Lithium rechargeables do not exist in AA size, because lithium rechargeables are about 3.3 volts instead of 1.5 volts (lithium ion for cameras and laptops are a different chemistry).
UPDATE: There is a new improved Energizer AA Lithium battery, less limited now. The current newest lithium AA battery is the Energizer Ultimate
, which is better, faster - those I saw recycled as fast as alkalines in flashes. If using a lithium AA, flashes will want the new one called Ultimate.
The previous data sheet (battery named "Advanced") previously said their current is limited to 2 amps for pulse loads, to prevent hazard. The current new L91 data sheet (battery named "Ultimate") now says 5 amps maximum peak, with about 3/4 the internal resistance, and seems as fast as Alkaline now, and should last much longer than alkaline in flashes. The lithium high internal resistance was artificially added as a safety factor. See their Application manual page 19-20 for reference of this safety protection (It says L91, but both were L91, each in their time. This document dated 2001 is the older version). Flash wants the new version called "Ultimate".
NiCd rechargeables - these still work of course, also a fast recycle, and they were great in their day, but we don't see them any more, because they only have a fraction of the capacity of NiMH (perhaps no more than 1/3 capacity of NiMH). Not a good choice today. A NiMH charger will be fine for NiCd, but an old NiCd charger is not right for NiMH today (I would replace it now.)
FWIW, here are approximate numbers I checked in a SB-800, using a Fluke DVM to measure current, and an iPhone video camera for the time to the Ready LED. I'm not claiming precision measuring the current amps for pulses, different tries see numbers a little different. It is not a constant value, it is a decreasing pulse (continuing weakly maybe ten seconds after the Ready LED). But this reading is suggestive of the scale. The difference between today and the 2003 SB-800 manual is the Eneloops and Ultimates.
| Battery | Recycle current | Recycle time |
| Eneloop NiMH | 6.7 amps | 2.9 seconds |
| Energizer Ultimate Lithium | 5.3 amps | 5.5 seconds |
| Duracell alkaline | 4.8 amps | 6 seconds |
Advanced AA Battery Facts
We might imagine that Alkaline batteries have advantage, being 1.5 volts instead of 1.2 volts for NiMH. However not so, the 1.5 V is very fleeting, not practical reality, and the other downsides are so great anyway. Over most of the batteries life cycle, the NiMH battery has higher voltage than alkalines. The graphs below are from the specification data sheets of two AA Energizer batteries, first Alkaline E91, then rechargeable NiMH NH15-2300.
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Energizer E91 Alkaline
from Energizer AA E91 data sheet
Note the Alkaline battery is hardly ever at 1.5V, and only above 1.2V during the first third of its life (if at higher loads). The voltage drops steadily until it is gone (about 1.0 or 1.1 volts for many devices). This is why recycle becomes very slow as the battery runs down. We likely discard them before it reaches bottom.
The Alkaline curve shows constant power 250 mW, and the NiMH curve shows constant current 230 mA, for both around 10 hours life.
But if we assume NiMH is constant 1.25V, then the power is 1.25V x 230mA = 287 mW. Very similar situations in these two charts.
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Energizer NH15-2300 rechargeable NiMH
from Energizer AA NiMH NH15 data sheet
Note the NiMH battery voltage is more constant, and above 1.2V almost all of its life. NiMH gives a generally flat voltage curve, until it is gone.
Simple battery charge status meters in our equipment just read the voltage. Designed to indicate the dropping alkaline voltage curve, this meter can't work right for NiMH - it will falsely start out showing only 1/2 charge for NiMH, but it will stay there all the time, until the battery is dead. My notion is this is why flashes don't have battery meters, not useful for NiMH cells. Longer flash recyle time informs us when the flash batteries are getting low.
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Internal resistance: Alkaline: 150 to 300 milliohms (recycles slow)
Capacity: Depends on discharge rate. The first data sheet bar chart shows about 2800 mah capacity at 25ma discharge, but only about 1300 mah capacity at 500 ma rate.
Also see the "Photoflash" in last chart on data sheet (shows 1000 ma for 10seconds/minute for 1 hour/day), for 100 minutes.
This must be for a tiny camera's flash, external speedlight current is significantly higher.
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Internal resistance: NiMH: 30 to 40 milliohms (recycles fast). This is what the flash recycle needs, does not limit the current.
Capacity: NiMH mah rating is specified for a discharge of ANSI 0.2C rate (approx 460 ma for this 2300 mah capacity.)
See FAQ #24.
The Capacity of a battery (example 2300 mah) is called "C", and a charge or discharge rate 0.1C means 0.1 x rated 2300 = 230 ma rate (for this 2300 mah cell.)
0.5C is a good charge rate for NiMH, which is 1 amp for 2000 mah Eneloops (good for best detection of full charge state).
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The NiMH battery is a really great thing, except for rapid self discharge. The Eneloops also solve that now. Note that the speedlight is exceptionally hard use, with battery current MANY TIMES higher than these data charts show (for a couple of seconds after each flash, while it is recycling). The
Eneloop data sheet does show a 4000 ma discharge curve (constant current), but my SB-800 speedlight at full power measures a recycle battery current of about 6.7 amps (6700 ma, Eneloop NiMH). It is a pulse of course, decreasing, not constant. My measurement (using a Fluke DVM) is not claimed to be a precise value for pulses, but is not likely overstated. This high current is why the batteries get hot, but speedlight recycle speed needs what NiMH can do.
Chargers
So, it would seem that any but casual use surely wants NiMH batteries in the flash. And if you want them to hold a charge a few weeks or more, get Eneloop class NiMH. And get a good charger too, which will properly take care of them. The cheap chargers are of a few types, a few just always charge at a low slow rate and never shut off. Some shut off after a constant time period, regardless of the battery size or previous charge state. Other faster ones shut off when the batteries get too hot, which implies charged. The better chargers have circuits to monitor battery voltage and state, and shut off when the battery is full. This is not just some simple maximum voltage like car batteries, instead the curve has a little hump after which the voltage falls slightly (called Delta V), and this is much less pronounced in NiMH than in NiCd, and also temperature dependent (see Eneloop data sheet.) It's not real simple, relatively difficult, and best performance requires some smart. Some of these monitor and control a pair of two batteries combined (without seeing individual detail). The better ones monitor each battery individually (multiple charging circuits with individual status LEDs for each cell slot). But the cost savings of recharging, instead of buying replacements every time, will easily repay the cost of the charger, and meanwhile, your flash can enjoy the better NiMH recycle speed and capacity. But do get a decent charger because the cheapest one is not a bargain. The flash performance is better with rechargables, and you can have fresh batteries at will.
I use and like these two chargers - both charge and monitor the batteries individually (four charging circuits), so each battery gets its full complete individual attention.
The Maha C401FS is excellent, and this one even operates on 12 volts from the car lighter socket while you drive. There are international versions, however this AC is 120 volts only (not 240V). Has the four LEDs for individual status. It has a switch for fast and slow charge. Fast is 1 amp for AA, which is the ideal 0.5C rate for Eneloops. (0.5C means two hours for a dead battery, but one hour is my more usual case).
The Maha C9000 is fancy, with the LCD which shows voltage and current, and total mah charged (for individual cells), and it also has a few modes (charge, initialize, discharge, analyze, cycle - see the C9000
User Manual). 100-240VAC operation. Its default charge rate (insert batteries and walk away) is 1 amp (ideal 0.5C rate for Eneloops), but individual slots can be set from 200 ma to 2 amps.
Copyright © 2012 by Wayne Fulton - All rights are reserved.
