Now that it's going to get darker earlier in the evenings, you need to make sure that your bike lights are working fine.
Yes, I did say lights, plural. The law requires that we have a bright front white light and a rear red reflector, but a better practice is to have a red rear light and a red rear reflector. I mean... what if they guy behind you forgets to turn his headlights on? No light to reflect. And, if your light malfunctions, at least you've got a reflector as a back up.
Personally, here is what I use in the darker months; a bright front light, a low mounted red rear reflector & non-blinking light combo device, and a seat mounted blinking red light (PlanetBike SuperFlash). Also, I wear an ANSI-approved highway worker's vest from AlertShirt.com, and reflective ankle bands. One of my bikes has two red SuperFlashes and an amber reflector in addition to the red reflector. Amber reflectors are 2.5 brighter than red reflectors of the same size, according to John Forester, but are not recognized by the law, unfortunately. So mine is there to provide additional support, it's not the "legal" reflector.
Does this sound excessive? It all a lot less expensive than an MRI, emergency surgery, Life Flight ($25,000?) or a funeral.
At the end of the day, I look at my lights before I turn them off. If they look dim, I check the batteries. I also check every 60 days on a schedule.
By "checking" I mean I pull the batteries out and put them on a simple DC voltmeter. If the alkaline batteries are running below 1.4 volts, I replace them. The batteries are still good for non-critical uses, but I just don't like batteries lower than that on my bike. If they are 1.0 volt or below, they are too weak for anything, and get tossed out (new alkalines start out at 1.6 volts or so).
Often, when a light is going dim, one batt is fine, but the other is dog meat. No need to toss both out, just replace the bad one.
For my bright white front light, I run rechargeable batteries, which I top off every week or two. My reason for not running rechargeables all the way around is that I don't want to spend my life charging batteries, yet I want to do something to cut down on battery disposal, so this is a compromise. Charging 4 cells at a time is OK with me. My charger, a Maha conditioning charger, holds 4. I do have some extra rechargeables so I could run the whole bike on them if I had to.
Now you see why the "no batteries needed systems" like on the Breezer Bikes hold so much appeal. For the habitual night rider, they can be convenient. However... they are costly systems, if (when?) the dynamo hubs go bad, then you're out quite a lot of money. Also, you can't move the lights to another bike. Lights are getting better, and it's hard to upgrade a fixed system. Battery lights you can move from bike-to-bike, which I do all the time. I have matching mounts on different bikes, and I just unclip and reclip the lights.
Even with all the lights, though, I don't burn through many batteries. Maybe 8 a year? That's not a big load on the environment, not compared to impact of driving my car.
LED lights are the way to go for entry-level AA or AAA battery lights. Real "bulbs" are old, inefficient technology that will waste your battery money. Now, higher-end "HID" lights with dedicated batteries are not LED, but they are in another price category. They are very bright.
The brightest rear taillight in the world is the DiNotte 140. I don't think I need that one yet. Definitely if gas goes to $15 per gallon someday and I have to bike commute all the way down SH6 with 50 MPH traffic. This one will keep them off my a**.