Mickeg,
I'm never averse to topping up from mains power for (re)charging gadgets when it is available. Like you, I use an outlet multiplier, but I also add an adapter that screws into a light fixture. Sometimes, it is impossible to get to outlets placed behind room furniture, but a lamp is almost always provided on the bedside table in most lodging and a screw-in adapter makes it a convenient source of power.
I also use a high-amperage multi-port USB mains charger that allows me to directly charge four gadgets at once at the fastest rate possible for each, minimizing the time needed to charge and the number of outlets required. Mine is the EasyAcc. Input is autoranging for international travel, so 100-240vac~ and 50/60Hz with output rated at 5.0vdc @ 4.0A total, distributed among the four outputs as: 1.3A, 1.0A, 2.1A, 2.1A. Obviously, not all outlets can operate at maximum draw simultaneously, but with a mix of devices, it has been fine. The plug folds in so there's nothing pokey/sharp that could hole a bag. USD$11 for the white version, both cheaper and easier to spot in a dimly lit pension than the black one:
http://www.amazon.com/EasyAcc%C2%AE-Charger-Folding-Portable-Smartphones/dp/B00LWRKAR8This has eliminated the need to get up in the night to swap items being charged from mains power on single USB charging port. My old strategy was lots of chargers on lots of outlets, multiplied as necessary to maximize charging. My new strategy saves weight, bulk, and needed outlets by using the multi-outlet USB charger. It works really well.
A reminder: A common cellphone USB charger can be used to also recharge other USB gadgets.
Photos attached below. You'll also see my Sanyo Eneloop USB recharger for AA/AAA cells. It does up to two at a time, and is a "smart" charger that works especially well with Panasonic/Sanyo Eneloop batteries thanks to a "pulse charge" circuit. I use standard Eneloops as well as their high-capacity "XX" versions for high-demand devices. My USB (re)charged AA/AA cells power my...
LED headlamp for wearing around camp at dark (toilet forays, cooking outside, reading in tent, fixing punctures at night)
LED red solid/flashing taillight(s)
LED white solid/flashing safety headlight (car drivers recognize blinking white = oncoming bike where I live)
SteriPen UV water purifier
Sony AM/FM/Weather radio
Garmin Oregon 400T GPS
Not all batteries are used at the same rate, so I don't need a full backup set. The most critical ones are those for the GPS and SteriPen, so I do carry a spare set for each. If I really needed to, I could raid spares from my other gadgets to power them.
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On a general side note...
Carrying a large pile (mains-rechargeable storage battery) is a viable alternative to a dynohub/dynocharging setup if you won't be away from mains power for long periods (days or weeks at a time). I use this alternative when touring with bikes that don't have dynocharging; it worked fine for me over 4 months' touring in Europe supplemented by one of my Joos Orange solar panels with a 5,400mAh accumulator battery. My battery is a 20,000 mAh rechargeable pile capable of charging and powering high-draw/high-drain devices including an iPad. I have confirmed both its capacity and efficiency in my tests. For use when touring with no other charger, it is good for three days or more of reasonably hard use before needing to be topped off again. It will power my phone continuously under heavy use for over 17 hours. It charges itself quickly and only from mains power; in 20 minutes it will grab enough juice to fully recharge my large screen smartphone from flat to full over the next hour while riding. This is particularly convenient when I have stopped at a cafe for a quick lunch and then need to get back on the road soonest. I'm not tied to the outlet back at the restaurant, waiting the hour it takes to recharge my phone from flat.
For many people taking shorter tours or touring in civilized areas, a large capacity rechargeable battery makes much more sense than a full dyno-charging setup when cost is figured into the picture. I paid USD$80 for mine at Amazon US, available for £49.99 in the UK. This is less cost than an inexpensive but effective "budget" dynocharging setup (i.e. Shimano dynohub in a built wheel from German eBay plus an AXA Nano headlight with USB charging), and a fraction the cost of a high-end dyno-charging system with lighting. It will also recharge any of the increasing number of USB head- and taillights, and serves as a source of direct power for extended usage.
After a lot of searching, I settled on the Anker 2nd Gen Astro Pro2 20000mAh Quad-Port External Battery:
http://www.ianker.com/product/79AN7906-BA ...and...
http://www.ianker.com/product/79AN7906-BA#sthash.cSlfbHwZ.dpuf ...and FAQ here:
http://www.ianker.com/product/79AN7906-BA#ptop I have confirmed its efficiency and rated capacity in my own tests and it has given good service. When its mains charging unit failed in France last summer, I found a common replacement at a small electronics store outside Amiens; Anker sent me a factory replacement promptly and without quibble upon my return home. It is a smart charger, capable of charging each of three USB devices (4.5A maximum among the three) hooked to it at the maximum allowable individual device charging rate as well as supplying 9v @ 2A and 12v @ 1.5A. It is compatible with all Apple and Android smartphones, tablets (including the Nexus 7) and other USB-charged devices.
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While I have used batteries about as long as dyno power, I usually prefer dyno-charging because I often take much longer trips into remote areas where there is no power. I also like the satisfaction of making my own power while I ride or supplementing it from the sun...and I like playing with various means of charging and powering my gadgets. I prefer dyno-powered lighting and carrying fewer batteries if possible. That said, I often supplement dyno-power with buffer and storage piles. Last summer I would occasionally watch a movie on the phone in my tent before dropping off to sleep. Similarly, I'd sometimes read just a single chapter of an e-book on the phone screen before dropping off. I never lacked the battery power to do so and it worked out fine for me.
I have standardized on USB-chargeable gadgets requiring a nominal 5vdc @ 500mA-1.5A. This was a deliberate choice so I could keep things charged under my own power or recharged with mains power using an adapter or large storage battery. Sometimes, it doesn't take much to adapt a gadget. My daily Panasonic electric shaver only needed a USB male end grafted onto the charging cord. I may replace my chemical handwarmer with a USB-chargeable one for use in really cold weather. The weight is the same, and no butane or other fuel is required. I have a standalone charger for my spare phone battery, so I have no downtime if my primary battery goes flat.
Initially, I did not expect to find much in the way of gadgets suited for my needs, but soon found solutions that worked and their power requirements did not compromise their usefulness. For example, my large-screen phone (bordering on a phablet) meets my own touring needs better than a full-sized tablet would, independent of the power requirements (it is smaller and stowable in a jersey pocket and always with me). I now do most of my non-analytical computing on it. I used it to write this.
For me, going to USB-powered devices reduced the number and size of things I take and a common power source means any device can be replenished from any charger. In my case, "any charger" means a USB source powered by dynohub, solar, mains adapter, or large capacity rechargeable battery. A similar case could be made for standardizing on USB-charged AA/AAA cell-powered devices. Things are getting better in that regard -- rechargeable batteries are getting better, and devices are now designed for greater efficiency. My AM/FM/Weather radio runs on one AAA cell and lasts ~65 hours. I have a small MP3 player that goes nearly 100 hours on a single AAA. Such great efficiency means fewer batteries to carry and more reserve charging capacity no matter how you go about it.
Best,
Dan.