I can't state how convenient hub dynamos are, no noise, no maintenance, unlikely to be robbed without stealing the whole bike, it just works, perfect for a city bike.
I get why people like them, but they make way less sense when you work out the capacity of an equivalent weight (not to mention cost) of lithium cells.
It's easy to get to about 90Wh, which will run a dynamo-powered light for 30 hours on max (most dynamos seem to be rated 3W).
There are definitely cases where it makes sense, and not having to keep batteries charged is nice, it's just easy to miss how good batteries are these days.
Not having to take the light off the bike and charge it and then forget to take it back to the bike, not to mention forgetting charging it and finding out when it's dark, is completely worth having a dynamo.
I live in Tokyo, and only drive in the city center. 90% of me having a light is the legal requirement of having so, I virtually never need it since the streets I usually ride are well-lit. The remainder 10% is that I like the solid feel of the bike overall and felt sad for the integrated light not to work TBH.
Can't emphasise that enough. Especially if you're into black clothing and have a black bike.
"This showed that for cars DRL reduces the number of daytime injury crashes by 3-12%. The effect on fatal crashes can be estimated as somewhat greater (-15%)."
A spare battery in your saddle-pack solves most of those problems.
If you're worried about being without light, a (typical) dynamo system is more complicated and exposed than a battery system, so will be more prone to failure.
I suppose you’re a casual cyclist and you don’t commute on a daily basis.
If you commute on a daily basis, a hub dynamo and light system is a bliss. Just hop on the bike and go. I have used bikes with Shimano, SP and Son for thousands of kms in all kind of weather and never really experienced a fault. It’s as simple as car lights - you just take them for granted.
With battery powered lights you need to take them off and put them back; recharge them; remember to bring them with you and not lose them. A spare battery pack is not enough (front and rear) and may not work during cycling (not all lights can be charged while turned on). And, low quality battery powered lights tend to quickly break (2-3 years) while I now realize one of my b+m systems is 10y old already. Good battery powered lights will probably last more, but they’re as expensive as dynamo powered ones.
So yeah, battery is ok and cheap for casual cycling, but very suboptimal if you want reliable lights every day throughout the year.
You're comparing a hub dynamo with cheap low-capacity rechargeable lights.
Rechargeable lights from the usual suspects are generally not good, they are expensive for what they are, have low capacity, and don't have swappable standard-size batteries.
They make dynamo systems look like a good deal, but if typical battery-powered lights were even close to their theoretical optimum I think people would be much less enthusiastic about dynamos.
Good lights last more (I have a Blackburn lamp and it’s working) but it’s still less convenient than dynamo. You need to remove and remount it every time, with the risk of dropping or forgetting.
Ofc if you mount fixed battery-powered lights and you could just swap a usb c battery, maybe it would compete with dynamo. But an easy swappable battery would still ve easy to steal (unless it’s inside the frame with a lock or sth like that)
Typical non-hub dynamo lasts like 30 years parked outside, and nice ones cost like $10 on Amazon. You smack it and they start whining at you. They are only barely more complicated than a stew pan.
Hub dynamos seem a bit more fragile, with a wire extending into the lightbulb, but never heard reliability is a concern with it...
I mean, it does have like, a wire between the hub and the lamp body. I think parent comment mentioned something about fragile wires when I posted the reply, I should have quoted it.
Exactly my setup, a nexus hub with 8 speeds, the bike has been outside under rain and occasional snow, and it's completely reliable for my daily work commute.
As mentioned, a city bike, I don't think a dynamo hub would be a practical choice for a racing bike or mountain bike, nor fit all riders.
The drag is not an issue for a bike that I use to commute to work and go shopping, the convenience out weights by far the drag, and if the worry was weight and drag there are other parts that contribute much more like the carry bags, pannier rack, mudguards that again, are convenient.
Another positive factor not mentioned would be environmental, no need to create waste with batteries.
I would imagine it's minimal. I'll never forget a demo I played with at a Science museum as a kid. A dynamo with a crank you can turn, and set of switches that allow you to turn on one, two, or three incandescent bulbs. The crank turns freely without load, and is increasingly more difficult to turn as load is added.
