I have a portable battery with two USB ports. One is labelled Android and one is labelled Apple. Apparently each has charging circuits optimized for that particular type of device. This sounds unlikely to me (both ports appear to charge my Android device just fine), but I don't know much about it, especially regarding Apple devices. Is there any truth behind this? What is the difference between the ports and can I charge any device using either of the ports? I've also seen tablet and phone specific charging ports. Do they simply differ by maximum output current?
There are two USB charging standards; the official one and the Apple one. You can get a copy of the offical one from usb.org. How charging works depends on whether you are connected to a computer, USB hub or wall socket. For the sake of this discussion I'll just talk about wall sockets, what the USB spec refers to as a Dedicated Charging Port (DCP). Per the USB2.0 spec, a DCP shall short the D+ line to the D- line and supply 0.5 to 5.0A at 4.75V - 5.25V. However, a device being charged cannot draw more than 1.5A. (http://www.usb.org/developers/docs/devclass_docs/BCv1.2_070312.zip)
Apple tends to do things its own way and the charger identifies itself to the device by the voltage it applies to the D+ and D- lines. A little write up is here https://learn.adafruit.com/minty-boost/icharging. An anecdotal story; I used to work for Nokia so had Nokia phones. I had a car charger that wouldn't charge the phone very fast but it was iPhone compatible. I pulled it apart and shorted the D+ and D- pins so to matched the USB spec and it then charged the phone properly.
One more thing to point out; it is the battery charging circuit in the device being charged that determines how much current it draws, not the charger. Of course if your device can draw 1000mA and you only use a 800mA charger then it won't charge as fast as it could but plugging it into a 1200mA charger won't make it charge any faster.
USB chargers supply 5v and are capable of 500ma. That much is standard. These days we have chargers with higher current capabilities - that is, they are able to supply more current if the device tries to draw more. An Apple compatible USB charger connects to the USB data lines as well, in a way that tells an Apple device what the charger's current capability is; that device in turn, only tries to draw that much.
USB chargers don't "push" current. They are, up to their current limit, (more or less) constant-voltage power supplies. Using a charger with a capacity for supplying more current than the device needs does not mean that it will push any more current at the device than the device can handle; that is controlled by the device. Using a charger with a lower current capacity than the device needs will reduce the charging rate, or the charger's voltage will fall as it tries to keep up and the device will be unable to charge properly.
I've done a little research on this (well I read the Wikipedia article on USB) and it seems that for fast charging there are two standards: the Apple one, and the non-Apple one. So yes, the two ports on your portable battery are different.
The real question is - does it matter? My experience is that some devices don't care which socket they are plugged into, and others do care.
For example: I just bought a no-brand wall-wart charger and it works great with my iPad (1.5A measured current), works slowly with my Android phone (0.5A) and works not at all with my Windows8 tablet. A bit of investigation with a multimeter showed that it is built to the Apple fast charge spec. Another charger which is non-Apple spec works great with the Windows tablet (1A), the phone (0.8A), and also to my surprise, with the iPad (1.5A).
My experience is that it does matter, but it's not so simple, because not all Android devices are the same. Some Android devices will charge just fine from an Apple charger, some will charge slowly (regardless of amperage), and some will not charge at all. Plus, I've found that there is some variability among the Apple chargers.
For example, I have a couple of Scosche USBC202M Dual 10 Watt car chargers that are pretty nice; they are mainly designed for iphones, and they work fine on my wife's iphone, and on my LG G2 (at the full rate, as monitored by Android Tuner Pro), but my Samsung Galaxy Tab 3 doesn't even register it as being connected, even using a charge-only cable or adapter. Yet I have another car charger, also made mainly for iphone, that works on all 3 devices.
I suspect that many newer Android devices may now be compatible, where they were not in the past, although I have no evidence of this.
Traditionally, and perhaps currently to some degree, Android devices will not charge at currents above 500 ma (USB standard) unless you use a charge-only cable, which shorts together certain pins to force it into higher current mode.
So, the bottom line is, it may work fine, it may work at reduced current, or it may not work at all, depending on brand. Much of the time, when people say it works for their device, they don't have a clue whether it's working at full output.
actually every apple device I saw, ONLY charges on apple's chargers and Macs, so I think the port is 'modified' to be used with apple devices, something to identify that the charger is from apple
But when we talk about android, anything with >4.5 volts will charge the phone, but it depends on the charging current, plus, I have a tablet that doesn't charge on PC because my PC gives around ~350, but that's for a tablet, the original charger is around 2A, the tablet puts a red " mark on the battery to tell you it isn't charging, but actually it's charging but the current is less then the usage.. Actually I notice it to charge some percents after hours, and if you turn the device off, it will charge but a bit slow
Android: will charge on >4.5 even if it says not charging
Apple: need the charger to be verified that it's from apple before it can charge
NOTE: I'm not pretty sure about apple devices because I haven't used much, maybe someone will correct me or maybe help you better