I use a different setup, which has no problem with either a handlebar bag or with an Arkel small "bar" bag attached to a Thorn accessory bar set below the handlebars:
> my light is a Cygolite which I've used for about 10-plus years. It has a built-in lith-ion battery. Weight? Um, "quite light" - 4oz, maybe? It has several modes -- I use the daytime flash mode almost exclusively. (I rarely ride at night -- too many hazards, and my eyes aren't good enough.) My light has about 420 lumens capacity, if memory serves. There are current models which offer about 600, up to well over 1000.
> the Cygolite has a nice swivel feature, approx 30º. It can be removed easily from its holder, so could be used as a flashlight. The holder clamps onto the bar, fixed in place by a sturdy plastic twistgrip allowing a finger-tight pressure. That in turn allows e to raise or lower the beam/flash as needed.
> to recharge this and other electronics: I have a SON28 dynahub hooked up to a Sinewave Revolution charger. The SON28 charges an Anker 5200Ah cache battery -- usually from 0 to full in 3-4 hours' riding, depending on the terrain. I charge my various electronic items overnight.
> I usually need to recharge: my headlight (roughly every 3-4 days on average); my phone (depends on type of use - typically every other night); two tail lights, one as backup (seatbag light has two rechargeable AAAs, recharged every few days); headlamp (3 AAAs every 2-3 days); and my Panasonic Lumix camera (maybe every 2-3 days, depending on use.
> I carry an adapter with a USB cord so that I can use mains power if need be.
I've used this arrangement for the past 6 years with no problems. Initially, I ran a headlight on my Raven, but that had priority for my SON's output, and I was unable to charge my cache battery while using the light. Also, the light I had mounted (an AXA item) had a crappy support bracket, which eventually fractured. Rather than replace it, I switched to the setup described above.
I've found this arrangement simple and reliable. Recharging just becomes part of my daily touring routine. When I'm at home, I get lazy, and just use the mains for anything that needs to be recharged.