...is replacing his battery powered lights the best way of doing the
Be aware that we can't answer this without mor information. I commute year-round in Minnesota and we have condition close to yours. Here are my thoughts and experience with dyno hubs:
I tried a dyno hub because I wanted what I thought was simplicity but when I executed the plan I realized that my assumptions were wrong and I switched to battery operated lights (which I will also discuss).
My first problem was one that your husband might also have - the wheels on my two bikes were a) different sizes and b) had different brake set-ups. Fair weather bike is 700c road bike. Winter bike is 26 inch mountain bike. (Add to this that I sometimes ride my 700c in the snow so I have two sets of wheels mounted with different tires.) I first tried to overcome the tire size by figuring out if I could run a 700c wheel on the front of the mountain bike. The short answer is that it wasn't worth it just to use a dyno hub. Add to that the 700c bike is rim brake and the 26er is disc brake. Again, if wheel size wasn't an issue this could be accommodated but also again is that it wasn't worth it just to use a dyno hub. So the two different wheel size thing is an issue. As a note though, even if the wheels were the same size and you could switch them between bikes the little connector at the hub (at least on the Shimano hub) is flimsy and not really designed to be connected and reconnected.
My second problem was that the lights themselves are hard wired onto the bike. First, see above about bike switching. Second I park my bike on the street. Even though I have an indoor garage I leave my bike outside. This is actually important in the winter but let's not go into that and not to mention that garages are some of the best places to mess with people's bikes! Plus, what about stops at the store or a meeting on the way in or out of work? So security makes me want to bring my lights with me. These things cost hundreds of dollars and I don't want them stolen. Now, modular mounts and connectors could be improvised (I looked into all of this, even prototyped some solutions) but with the wheel conflicts (and don't forget - mittens!) I threw my hands up.
What made me sell the wheel was that one day in the dark when the connector failed. Or maybe a broken spoke sends the wheel to the shop for a day or two. Or maybe I was running late one morning and my bike had a flat so I grabbed the other bike. Whatever, you get it. I needed to have battery back-ups and those back-ups needed to be as good as the dyno powered lights!
If you are not sold yet, imagine changing a flat and then trying to get that hub connector to work when it is below zero and dark. You need to fold those little wires... your fingers will freeze. Guaranteed.
What I settled on:
I bought the most expensive taillight that I could afford. It was hundreds of dollars and come with so many mounts that I have a mount on six bikes. The light charges via mini_USB and can run off of an external battery. I am going into my sixth winter on this light; totally worth it! It has multiple modes (of course) and slips on and off it's mount quickly but securely. (See note below about mittens!) I also keep some 1 watt "blinkies" in my bag for back-up and I ride with a small blinkie on my helmet.
For headlights I use bright LED flashlights from China which run on 18650 batteries. This battery system is so much better than AA batteries. They are not in the same ball park. They are not even playing the same sport! One battery per light gets hours of run time and if it runs low you pull a new one out of your pocket. That's one - one battery per light. The lights get cheaper and smaller every year. The mounts are plastic and velcro and cost less than $2. They take ten seconds to apply and I can do it with winter gloves on. And by gloves I mean mittens that provide the dexterity of boxing gloves.
Of course you can get the super-bright LEDs that have cords and battery packs; I have tried them and do not need them. Flashlights work great, I can carry spare lights and batteries easily and it's all swappable. I have a charger at work and at home and the batteries are cheap and abundant. I also ride with a small blinkie headlight that I velcro to the top of my helmet; easy on and off and charges via USB.
As I said, independent lights let me ride any bike any time and I can leave my bike anywhere.
I can post links to any and all hardware but this isn't an advertisement.
I use the taillight from Dinotte. The Quad RED is the current offering but I am still using the 300R that I bought in October 2010 which is still going strong.
For bar-mounted headlights I use flashlights from Solar Force. The flashlights I use run on one 18650 battery. I am not going to lie, the website is confusing and once you figure out the website the individual parts you need to order are confusing and once you figure out which parts you need to order figuring out the options of the various parts is confusing. However, this is the place to get quality lights for cheap. I use the L2N body with the 3.7v XM-L T6 Cree bulb. (I also order extra switches and reflectors while I am at it but they are unnecessary. However you might want to test an orange peel reflector which diffuses the light; if you run two headlights one with orange peel and one with smooth provides flood and spot lights).
I mount the flashlight using these velcro mounts.
These mounts are great for all bikes but on my winter bike I actually have a rigid mount that the lights snap in and out of, something like this but without the 180 swivel feature. I use hose clamps to attach the mounts to my handlebars. It's not pretty but in this regard I am all about function. I can mount, remove, and adjust the lights while wearing mittens.
For charging the 18650 batteries you should make sure you get a smart charger and just read up on which product tends to be best reviewed at the best price. Right now the Nitecore D4 is doing pretty well and has the bonus of being able to charge a bunch of different battery sizes. In addition to the smart charger which I keep at home I also have a simple charger ($10 or less) at work.
For blinkies I am using Blackburn Fleas. I picked these because they charge via USB (or solar!) and use the same charger so I can have one at home and one at work. The charger is proprietary otherwise this would not be an issue. I really like the Flea headlight because of the way I use it. I use velcro to quickly stick it to the top of my helmet, no straps to mess with. It is built in such a way that I am able to remove a bunch of plastic from the bottom (shave it off with a razor knife) to lower the profile.