I have a Neewer NW670C flash which uses 4 AA batteries. I've been using regular alkaline ones so far because I couldn't get myself to buy rechargable ones yet. However, the flash ate their capacity in no time.

Now I got rechargable ones. Ni-Mh 1.2V 2000mAh. They are fully charged at 1.41V each, yet my flash won't power on. Not one blink, not even the LCD, not a "lo-ba" sign, nothing.

I've tested the regular alkaline batteries which are still able to power the flash (they are on the empty side though): 1.28V per cell. That's less than what my charged Ni-Mh's offer.

With 4 cells combined I'm looking at ~5.12V alkaline (works) vs. ~5.64V Ni-Mh (doesn't work).

Can I not use rechargable batteries inside a flash? Do I need a special type?

Another thing that surprises me is how external flashes tend to not have a 6V DC input. Can anyone explain why that is so? I understand the front power input is for ~230V to directly power the flash (and still requires you to have the batteries to power the circuits etc. of the flash), so that's out.

It'd be so much easier to simply plug a 6V DC power-supply. Why aren't we given such option?

Update (2019-02-17): Thanks to everyone for the great answers. My local drug store recently got some new rechargable batteries which caught my eye instantly. They were really cheap ($5 for 4pcs) and what was on the box looked promising: 2.400mAh and labeled "for use with high current applications". Even quick charge supported! They are regular NiMh 1.2V ones.

Thinking I can't go much wrong with that price, I bought two packs - Ran tests on them with my battery tester - They actually have 2480mAh. Tried them in the flashes: Voilá. I've now had a guessed 300 flashes on 1/16th power since the last charge, still no low battery warning.

  • The best place for information on the subject would be....the manual. What does it say? Ore only LR6-type batteries supported or are HR6 supported as well? As to Another thing that surprises me is how external flashes tend to not have a 6V DC input. Can anyone explain why that is so?: We can't see into why one manufacturer does or does not offer a feature. My personal opinion would be: To have a unique feature for their flagship devices. But no company would ever state this - even if it was true. – flolilo Dec 6 '18 at 12:51
  • @flolilolilo Manual says "Alkaline or Ni-MH are usable". – confetti Dec 6 '18 at 13:09
  • "Why aren't we given such option?" You are with a "studio" flash. "Speedlights" are made specifically to be portable and untethered to electrical outlets. – Michael C Dec 6 '18 at 14:35
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    If the manual says Ni-MH work, then I'd try them one more time, and double check that each battery is inserted in the correct +/- orientation. That wrong orientation is the common reason for AA batteries not working at all. Ni-MH is a bit less volts than alkaline, but when under usage load, the Alkaline fall much lower very quickly, whereas the Ni-MH remain steady at 1.2V for their entire capacity. This is a plus, not a negative. – WayneF Dec 6 '18 at 15:00
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    Not only will it work, but it will work better as well. Ni-MH battery has better high current discharge characteristic than alkaline battery and will give you a shorter recovery time. – user3528438 Dec 6 '18 at 17:18

Although freshly charged NiMH measure at 1.4 or so volts, they quickly drop to 1.2 under load. However, unlike alkalines, they stay around that 1.2 for a long time (this is called a "relatively flat discharge curve").

Alkalines by contrast have a much steeper discharge curve but do present a higher terminal voltage when new. (Hint: You can separate unused alkalines from somewhat-used ones with a digital multimeter. The unused ones should measure 1.6V or so.)

Either way, your flash seems to be absurdly sensitive to battery voltage. No doubt the reason your flash "uses up" the alkalines so quickly is that they have dropped below the voltage the flash is happy with. There's likely still plenty of energy in them.

Conclusion: Maybe the flash is defective but I bet it's just a poorly designed unit. I have never had a flash that failed to work very well with 4xAA NiMH cells. This includes camera-maker-brand flashes "dedicated" to my camera, other-maker flashes also "dedicated" to my camera, and some "vintage" Vivitars that just do "auto-thyristor" mode with their own sensor.

Aside: I wouldn't trust Ikea brand batteries of any type. Nor any other store brand. Big chain stores pay the real battery manufacturers to wrap their store name on whatever batteries are cheapest this month. otoh I've had absurdly good results from not-nationally-advertised-brand alkalines, and far less leakage than from one of the best-known name brands. Your results may vary.

For NiMH cells, from my experience, I'd try Panasonic (Eneloop or not, your choice, Eneloops are low self-discharge but lower energy storage), Tenergy, or Powerex (Maha). Powerex/Maha also make some of the best NiMH chargers available.

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    Thank you for your answer. That might very well be it and does explain the quick "use up" time (it's been just ~200 flashes on 1/16 power with new batteries. That's half of what the manual says.). The last point is good too, but I have a decent battery tester and the IKEA ones seem actually nice. I'll get my hands on another flash (same brand and model) soon and will test again with that unit. In addition: The alkaline batteries that the flash considers empty are at ~1.28V/cell, doesn't sound entirely empty to me. – confetti Dec 6 '18 at 17:26
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    Worth noting that NiMH batteries are almost without exception the batteries of choice for speedlites. Panasonic Eneloops, particularly, are widely well-regarded as the professional standard. They last longer, recycle much faster than awful alkalines (and can recycle more frequently), they run much cooler, and they're rechargeable! I don't think you'll find even a semi-serious amateur with alkalane batteries in their flashes except perhaps as a secondary backup for emergencies, so they definitely work fine in nearly every speedlite on the market. – J... Dec 6 '18 at 18:25
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    Yeah, generally speaking NiMH's flat discharge curve and current handling ability makes it better than alkaline for high-current applications like flash. A unit that doesn't like them is a dud. – hobbs Dec 6 '18 at 21:20

I use them all of the time in several different hot shoe mount flashes. The only difference I've noticed is that when I put in a set of fresh alkalines, the battery level indicator shows 'full'. When I put in a set of freshly charged NiMH batteries, the indicator does well to show three out of four bars. However, a set of fully charged NiMHs that show three bars will last longer than a set of alkalines that show a full four bars.

The Neewer NW670C is listed as capable of using Alkaline or NiMH batteries. I would start by trying a different set of NiMH batteries from a different source. If you have the capability to test actual battery capacity, my hunch is that your 2000 mAh batteries aren't really 2000 mAh. There are a LOT of cheap NiMH batteries in circulation that have vastly overstated capacities printed on them.

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  • I'm aware of the fake-battery situation. Those are from IKEA, quite reputable I'd say. They actually have around 2040mAh according to my charger. I'll try to get my hands on another set though to confirm. – confetti Dec 6 '18 at 14:48
  • I use 2400 mAh NiMH batteries. – Michael C Dec 23 '18 at 23:37

A 6VDC power supply would actually have to be quite massive (think laptop rather than phone power supply sized), big speedlites can draw several amperes when charging.

There are a few older flashes that, as per the documentation, deprecate the use of rechargeables (eg the Metz 45CT); this should not be an issue with more modern ones.

The most likely cause is contact problems - the rechargeables might be just a bit mechanically shorter than your alkalines, or their contacts might have oxidised (which will cause problems with a high amperage load) - try cleaning the contacts (on the battery and on the flash).

If this is not the case, either that flash is broken by design (that is why the alkalines also don't last worth anything, since - as mentioned in another answer - they quickly drop to 1.2V too), or actually designed for lithium AA cells (similar to, say, the Kodak Z8612IS camera, which does take standard alkaline or NiMH AAs but lasts maybe 40 shots on them) , or your copy has marginally defective electronics.

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  • The batteries are new, so contacts shouldn't be an issue. I've compared the size and it's the same. As per the PSU, sure I wasn't thinking small, but given that generally AA batteries can't supply more than 4-6A it shouldn't be that much of a problem. Especially since the flash has an internal capacitor I'm sure even a 2A power supply would suffice, at the expense of longer charging times of course. – confetti Dec 6 '18 at 14:19
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    To the contrary, NiMH can deliver significantly higher current than alkalines. For debugging flashes, a current limited lab supply is golden, can you arrange access to one? – rackandboneman Dec 6 '18 at 17:09
  • I can, but IIRC it has a maximum output of 24V 2A, so im not sure if that'd suffice or how to connect that to the flash at all. Voltage and Ampere are adjustable and there's a CC/CV switch. – confetti Dec 6 '18 at 17:21

If anything, rechargables should be better than alkalines because they can deliver more peak power. But that is a problem too, because they could cause a fire. Cheap toys refuse to accept rechargables because it would be unsafe. How do they know ? The + cap of a rechargable is a bit wider than a regular battery, so with a bit of extra plastic around the + of the toy it won't make contact. That extra plastic is there for your safety.

I find NiMH batteries to be unreliable. If you haven't taken good care of them then they won't hold much of a charge and won't deliver much power. A good charger that can do repeated discharge-charge cycles can tell you about the remaining capacity of each cell. One bad cell in a set of 4 can make the whole pack useless. Always bring spares, and spares for your spares.

The older NiMH batteries have a high self discharge, you can't keep them in your bag for many months. The newer low-self-discharge ready-for-use types (Eneloop etc.) have a lower capacity. I have seen failures with both types, or maybe I just need to upgrade to a better charger.

Finally, the discharge curve of rechargable batteries is different from single-use batteries. They hold their voltage longer, but at the end it drops more abruptly. There is little or no warning that they are almost empty, it comes as a surprise. Again, bring spares, even keep a set of fresh alkalines in your bag.

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Try getting NiMH batteries intended for high current usage. For example, get eneloop pro (capacity 2500mAh with 500 specified charge cycles) rather than eneloop (capacity sth like 2000mAh with 2000+ specified charge cycles). They will last fewer total shots over their lifetime, but will deliver more per charge and will recharge the flash much faster.

The clincher basically is whether the startup current of the charge circuitry will draw so much current that the voltage drops below the voltage where the logic circuitry can still operate reliably. If it drops out and, for safety reasons, disables the charge circuitry when dropping out, you have a hen-and-egg problem for startup.

Generally for devices with a flash (either cameras with built-in flash or standalone flashes) I use the higher-current eneloop pro.

If you don't want to hop on the brand hype of eneloop, at least try looking for batteries that have among listed use cases cameras/flashes and motor toys (which also take a bunch of current) rather than just alarm clocks, wireless handsets, and similar devices with low power demands.

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  • This is a very good answer. Thank you. I never got to update this question with what I ended up doing, I will do so now. – confetti Feb 17 '19 at 23:00

This is one of the most ignorant answers I have ever written, but I will keep it posted in case it helps somehow.

In my opinion, it is not about the voltage, but the mAh.

I only use 2500mAh batteries (1.2V). I tried once 1800mAh(same brand) and they did not work.

According to my experience then, a 2000MAmp battery is too close to the ones did not work for me. :o(

I am sorry I can not give any technical explanation, just experience in my case.

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  • That's really weird. You're confusing mA (milli-ampere) with mAh (milli-ampere-hours). The 2000/2500/1800mAh gives information about the maximum capacity a battery can hold. mA, or A (ampere) on the other hand gives information about the current the battery can supply, and varies from battery to battery, but should be around 5A max. for short periods of time. So in your case I'm sure there were other factors involved as to why 2500 would work and 1800 doesn't, as this difference only matters for the capacity (and therefore the max. flashes you'd get out of them). – confetti Dec 6 '18 at 19:10
  • True. I corrected those letters. Although I know my answer is totally ignorant, I will leave it if it helps somehow. – Rafael Dec 6 '18 at 20:40

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