Perhaps because of difference in voltage? Seems strange to me.

I don't think it will be the voltage because the chargers normally work on around 100-240 volts just fine.

Is it an original charger?

I don't think it will be the voltage because the chargers normally work on around 100-240 volts just fine.

Is it an original charger?

Confirmed, the charger works worldwide.

Try another charger. They do malfunction and go bad. Make sure that the charger that you use is putting out 2.0 maH or more. Computer shops should have a tester.

You mean amps, not mAh - an iPhone needs at least 1A to charge, preferably 2.

I suspect the OP may be using a substandard charger or a computer USB port.

What model iPhone?

What charging method are you using?

What are the specs on the charging unit?

Can you frame "ridiculously slow" in standard units of time?

Using a ~ 2 amp output (with 5 V DC) you start to approach the iPnone 6/Lightning capacity of 12 watts. If you are using a 1 amp supply then it will take at least twice as long.

It charged faster in the U.S. than here, using the exact same charger? Not sure that makes any sense.

Some external battery packs have two USB supplies, one with 1 amp output and the other for 2 amps.

Maybe read up on your iPhone mode/slow charging. This seems to be a common problem, with multiple causes and solutions.

Chargers rated at 1 Amp charges very slow compare to the 2 Amps one. Make sure the charger is not very warm or hot, it may be defective if it is very warm to touch - cheap no brand chargers tend to have a high defective rate. Voltage don't make a difference as pretty much all chargers are rated 110-240v. I've learn my lesson with cheap no branded chargers, pay more and buy a branded one.

This is the originally charger. It is for an iPhone 5. It took 2 hours to go from 50% to 100% charged.

It took 2 hours to go from 50% to 100% charged.

That's not so bad. If you plugged in via the USB it would probably take about four hours.

In the US it would take me 20 minutes to go 50 - 100%. ??

I have had many iPhones and they certainly don't charge from 50 to 100% in twenty minutes.

In the US it would take me 20 minutes to go 50 - 100%. ??

Perhaps thats because power is bigger & better in America

In general to conserve battery and decrease charge time,,

1) Double press home button

Swipe to close all apps frequently

2) Turn off wifi if connecting via cellular

3) Put phone on airplane mode when charging. It turns off all services and charges 40% faster. Remember to turn on when finished.

I have experienced similar poor charging and believe it to be defective charger and or cord related. Genuine apple charger and cord from 100% reputable supplier is my recommendation.

In the US it would take me 20 minutes to go 50 - 100%. ??

Perhaps thats because power is bigger & better in America

Lightning port may or may not have collected dust.

In the US it would take me 20 minutes to go 50 - 100%. ??

Perhaps thats because power is bigger & better in America

Always funny what idea users have about charging a phone battery.

All charging happens through some type of AC/DC adapter.

The 110 V (US) or 220 V (Thailand) AC is converted to some low voltage DC (like 5V at a USB port).

The required power is less than what you need for a neon tube.

From the previous post:

Lightning port may or may not have collected dust.

That is one of the hints that you find when you do the obvious "google research" for "iphone charge slow".

Others are about a SW update, failing "lightning" cables etc.

As I don't have and will never have an Apple product I am dependent on Google in this case.

After reading through a stack of those iPhone charging troubleshooters I happily returned to my cheapo Samsung

It charged faster in the U.S. than here, using the exact same charger? Not sure that makes any sense.

Upon reflection, increased ambient temperatures might increase charging time, perhaps even approaching 2X (at either/both extreme)?

High temperature/overheating of the charger might be a factor.

Could also kill the battery quicker than in low temperatures.

But that's all speculation without measuring/testing.

Hm, looks like the problem is that it's an iPhone.