Battery powered dynamo lighting

Did you know that many dynamo bike lights can be powered quite happily by ordinary DC batteries?

It’s only recently that manufacturers have finally started producing battery-powered lights with asymmetric reflectors, so you aren’t riding along spraying half your photons up towards the International Space Station.

The Busch & Müller Ixon IQ (£70) was the first decent effort that I’m aware of, and more recently the catchily-named Philips LED Bike Light (RRP £110) and the Supernova Airstream (an eye-watering £170).

Cycling off
Cycling off by Phil and Pam, on Flickr

If you already own a decent dynamo headlight, however, or are too just cheap to pay a lot of extra money for a proprietary holder with re-manufactured lithium rechargeables inside, there is a third way.

My headlight for 2011’s Paris-Brest-Paris and qualifying SR series (and for commuting through Edinburgh city centre) is the plain old B&M IQ Cyo. I bought it brand new for £35 online, and immediately set my mind to making it work with DC power, as at the time, I owned no dynamo.

B&M do advise that this can be done – it wasn’t completely heroic. In the end it required no great trickery. Wire the tail-light connectors of the Cyo into a plug that will fit your battery of choice, and switch the battery on. Shazam!

I’ve used several different battery solutions now – the 8.5V Li-pol rechargeables from my original Ay-Up mountain bike lights, a 7.5V radio control car battery, and most recently (for PBP) a simple AA battery holder, which I bought from Maplin for a couple of pounds. I tested this successfully with up to 6AA lithium primary batteries (a shade over 10V) and it was quite content.


You don’t get the same light output from rechargeable cells as you do from a proper dynamo, especially at lower voltages (I would want to use seven NiMH AAs, as they’re only 1.3V a pop). Also, importantly, one polarity of connection to the battery will be much brighter than the other, so test both. I’m not sure if there’s any ill effect of riding with the battery the “dim way around” but what would be the point?

However, that’s just the beauty of this set-up. You get stupendous battery life – I rode 1200km / four nights of PBP on just one change of AA cells – while the asymmetric reflector ensures that the available light is distributed in such a way as to make the most of it.

The current draw of the light (and hence both the brightness and the battery life) is strongly linked to voltage. At 7.4V my Cyo draws 190mA while at 8.2V it draws 290mA. At 9.8v (6AA lithium primary cells) it draws 500mA, which is nominally what it draws from a hub dynamo.

It’s easy to convert current to battery life for a battery of any given capacity. For instance, the 2100mAh LiPol batteries from my Ay-Ups will drive a 290mA light for ~7h15m (capacity / draw, or 2100/290). A cheap NiMH 6-cell pack will drive the lights for a healthy 12 hours – enough for two summer nights of near-constant use.

While clearly less bright than the lights of some (for instance, I have a 900 lumen torch from eBay), it is still a serious bit of kit. It allowed me to ride over 30mph in the middle of Normandy at 3am, which is good enough for me… if you want to go off-roading, you’re not reading the right article!

2011-08-24 at 03-01-28

In fact I doubled up on PBP and wired my Ay-Up MTB LEDs into the same circuit (using a different switch) so that if I did need extra light, I could temporarily flick on a ‘high beam’.

Most of the use this second light saw was just to economically “encourage” sleepy randonneurs into the side of the road (the big light overhauling them from the rear had a very useful effect).

As a bonus, I was able to run my dynamo taillight quite happily from the same battery, so I had a complete solution to my lighting needs with just a handful of AA batteries (don’t rely on being able to buy any on PBP though – other randonneurs may have clear-felled the battery landscape for miles around!)

If you’re interested in this, there is a pretty detailed discussion on the YACF forum about my experiences, including a few false starts, false stops, and general befuzzlement.

Bottom line: your B&M dynamo light isn’t just limited to bikes with dynamos, and it might even be one of the smarter choices out there for an ultra distance battery light!

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12 thoughts on “Battery powered dynamo lighting”

  1. Great information Dave. I have 2 new ‘B&M cyo IQ senso T’ lights which I had hoped to run via a 6V regulator from my 48V velomobile power assist battery until I discovered this; I am buoyed by your article if it means that I don’t have to send these lights half way around the world for a refund. Did you connect your tail light connectors rather than the dynamo ones to your battery?

  2. Hi David,

    I believe it’s quite common to run two IQ Cyo lights from battery in the velomobile world (see i.e. for a real world example).

    If you needed any further reassurance you could probably get hold of someone who runs a very similar system to your own (electrically) by posting on one of the recumbent forums like BentRider.


  3. Have a Magicshine light and the head unit is dying. Battery pack still seems ok, I am tempted to get the B&M light to link up to the Magicshine battery which kicks out 7.4v. Am I right in thunking that this would be similar to your set up? Ie the light is slightly dimmer than if run off a dynamo but bright enough for night road rides (I only have to navigate the rural lanes of South Devon after a late shift).

    1. Hi Chris, that sounds about right. Not much over £30 for a Cyo from Rosebikes so it’s worth a shot I think.

      I was happy with mine for a long time, although eventually I build up a Shutter Precision dynamo wheel when my Ay-Up battery connectors got dodgy.

  4. Seems this is the ideal halfway house – buy the light, run off my existing Ayup battery till I can afford the new front wheel with Dynamo! The beam pattern of the German approved lights is what I’m after as most LED lights around simply throw massive of amounts of light down range in a big spread, blinding all drivers and aircraft within 10 miles. I need good beam for commuting down from Glasgow over the moor with no streetlights in sight and speeds downhill of well over 40kph. The Ayups throw lots of light, but half is in places I don’t need it (Right hand hedgrerow).

    1. Highly recommended… this is exactly what I did, then eventually used a Maplin 5AA battery holder, then finally a dynamo. Now have three dynamo bikes and no battery ones!

  5. Maybe a silly question – is there any reason I shouldn’t do this on a B & M Lumotec Lyte+ ?

  6. Richard – very late response, but no. I’ve run a Lyt and taillight from a PP3 quite happily.

    Interestingly I used the inputs and weird the tail light normally to the tail light terminals.

  7. I have an ebike with a 12v battery I use for lights, and was trying to get a B&M “Lyt” to work as a “dip” beam as I have a massive splash LED for main beam. So far I have not had much luck, it will run on other batteries as you have observed up to about 8 volts, but the over voltage protection (I think) stops it working at 12v. This is weird as an unloaded hub dynamo will go right up to 50 volts on a down hill run. But I do not really understand volts vs amps very well.

    I have ordered a “buck convertor” to lower the 12v to 6v, and hopefully this will work OK.

    I have dynamo lighting on all of my bikes except the ebike, it is the best thing since sliced bread. “Taylor Wheels” do some very cost effective ready build dynamo wheels. I bought one of these for my wifes bike, and they are as good as I can build myself (well better actually).

    Great site.

  8. I have an inkling that a dynamo headlamp is way more efficient than a battery powered one. Most dynamos will produce 3 watts, so you can imagine that some of the top end B&M headlights are very efficient.

    I have an 80lux cyo and it is comparable with a 10w LED floodlight perhaps even brighter. So when running off batteries that is surely an advantage.

    I agree that 5 x AA or AAA batteries is the best number to run these on.

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