Portable charger

Assuming you mean a USB charger for a phone/tablet etc. Buy one when you get there. It will have the correct plug on it and you won't have to bother with an adapter.

A power bank?
https://www.amazon.com/gp/product/B06XJF53ZF/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

I am guessing he means a portable battery. Just about anything will work. I have a horse of a battery that will recharge my cell phone several times and a pretty good recharge on the ipad. It was gift but I don't take it on European trips because it weighs almost a pound and half. But it is handy when traveling in the US. Any electronic store will have a dozen to choice from. The speed about the same. Bigger and heavier means more juice. The one I travel with is about the size of a small cigar and will recharge a cell phone and an internal camera battery. I primarily carry it for the camera. I don't there is much difference in brands or performance.

I just bought whatever they had on the rack at my local Office Max. Its a Duracell. Its not a high tech item so not worth overthinking.

Go to Amazon and look for Anker Portable chargers. A smaller one is https://www.amazon.com/Upgraded-Anker-Candy-Bar-High-Speed-Technology/dp/B06XS9RMWS/ref=sr_1_7?s=wireless&ie=UTF8&qid=1534642125&sr=1-7&keywords=anker+portable+charger. This one is lightweight, started carrying it to top off our Iphones during the day.

Or you can go with this one https://www.amazon.com/Portable-Charger-Anker-PowerCore-20100mAh/dp/B00X5RV14Y/ref=sr_1_5?s=wireless&ie=UTF8&qid=1534642125&sr=1-5&keywords=anker+portable+charger. This one probably will charge all of your devices for multiple times before you need to recharge, but it is heavier.

We have both and are happy with them.

I have a mophie. I can't give you technological information about it as I'm no IT person. I just like it and it is conveniently shaped and sized. It charges my phone and iPod several times before I need to charge it. It's the size of a small phone. YMMV

Both daughters who were working for competing cell phone companies recommended Mophie -- about the size of a deck of cards. We carry it at home and abroad.

Thank you everyone! I think we are going with Ed's recommended ones! It actually is not for Europe, but for our trip to DisneyWorld this December.

This is the one I am planning to purchase:

https://www.amazon.com/gp/product/B0194WDVHI/ref=ox_sc_sfl_title_8?ie=UTF8&psc=1&smid=A294P4X9EWVXLJ

I notice you live in Eagle River. I was military in Anchorage in 1963-64. It was great.

You should buy 20000 mAh power bank. best for your trip.

Note FAA restrictions on Li-ion batteries on-board aircaft. Spare Li-ion batteries must be carried in carry-on baggge and not checked into the cargo hold. Li-ion batteries are limited to 100 watt-hour capacity with no more than two larger (101 to 160 watt-hour) batteries. (Watts = Amps * Volts).

https://www.visionsafe.com/2018/02/06/portable-charger-catches-fire-in-plane-for-second-time-in-a-week/

Portable charger catches fire in plane for second time in a week
FEBRUARY 6, 2018

A US domestic flight was forced to divert when a passenger’s lithium
battery caught fire, injuring two people and spreading smoke through
the cabin. Frontier Airlines flight 1883 had departed from Orlando in
Florida, destination Phoenix, Arizona, at 8.40pm on 3 February. During
the climb, a passenger’s battery that was connected to a smartphone
ignited. It burnt the owner, who knocked it to the floor. Another
passenger managed to pick it up and take it to the bathroom to place
it in the sink, burning his hand in the process. The battery was
covered with ice to try to cool it. The pilots decided to divert to
Tampa, where the Airbus A320 landed safely about 40 minutes after
take-off. The two injured passengers were give treatment for their
burns.

https://www.aeroinside.com/item/10976/frontier-a320-near-tampa-on-feb-3rd-2018-lion-fire-on-board

Frontier Airbus A-320 near Tampa on Feb 3rd 2018, LiOn fire on board

Updated: 2018-02-04 16:43:10 GMT

A Frontier Airlines Airbus A320-200, registration N221FR performing
flight F9-1883 from Orlando,FL to Phoenix,AZ (USA), was climbing
through FL300 out of Orlando when the crew reported smoke in the cabin
and decided to divert to Tampa,FL (USA). The crew advised that there
was smoke in the cabin believed to originate from a LithiumIon
battery, the cabin was on oxygen, the flight deck was not on oxygen.
Later into the approach the crew advised that there had been an actual
fire, the fire was now out. On final approach in contact with tower
the crew advised they wanted to taxi the aircraft to the gate and have
emergency services board the aircraft at the gate, the fire was out
for now. The aircraft landed on Tampa's runway 01L and stopped on the
taxiway while a gate was being sorted out. After the gate was assigned
the aircraft continued taxi with emergency services in trail, the crew
advised the device had been put on ice in the forward lavatory and
should be recovered by emergency services from there.