Sometimes it seems like it takes forever to get a device charged up. It's possible that the battery could be going bad but it's more likely to be something else. Fortunately, it's probably something easy to fix.
This is a very simple Instructable that won't cost anything and will only take a few minutes. If it doesn't fix the problem it should at least give you a better idea of what is going on.
Step 1: Gather Your Chargers and Cables
If you know which charger and cable came with your device set those aside we will test them first. If you don't know or don't have them - no problem
Step 2: Download Some Free Software
Go to the App Store that supports your device and search for "charge rate" or "battery monitor". You should find a number of apps that will read your battery/charge controller and show you the info. Not all software will work with all phones although I have never had any trouble finding one that works for the phones I have used.
For this Instructable I used the free version of Ampere
Install the software and fire it up to make sure it works on your device
Step 3: Get a Baseline
If you have your OEM charger and cable connect them up to your device and open the app you downloaded.
If you don't have your OEM components just pick the charger and cable you think works the best.
You will get better results if the battery on your device really needs a charge. That's when it tries to draw the most energy. It should be at least half empty.
Step 4: Test Your Chargers
Now we have a baseline or benchmark we can use for comparison. We want to keep one component constant while changing out the other.
We will use our OEM/good cable and test it with each charger. When you connect them to the device give it a little time for the charging rate to stabalize
If you have a lot of chargers you may want to mark them somehow to keep track of the best and worst ones.
Step 5: Test Your Cables
You can guess the next step. We take our best charger and use it to test each of our cables. There can be big variations in the quality of chargers but even bigger variations in cables.
Once again I encourage you to keep track somehow of your results. If you have a lot of cables make liberal use of the circular file.
Step 6: Finished !
You should now have a much better idea of how good of a match your chargers and cables are for your device.
It's hard to look up what your charge rate should be but pretty much all phones and tablets in the past few years will charge at at least 1A, things like iPads usually charge at 2.1A
There are a whole new group of fast charge "standards" like Quick Charge out there that can pump up the volts and amps. The actual numbers for V and A may change but the testing process is the same. You are not comparing your results to some kind of goal but to what works best for your device.
I hope you found the component that was slowing down your charge.
Step 7: For Enquiring Minds . . .
A little more explanation:
In your phone/tablet you have a battery, it is connected to a charge controller. That circuit is in charge of managing the flow of energy into and out of the battery. It's programed to meet the needs of that device. The external components are the charging cable and the charger. The charge controller has some "intelligence" that allows it to gauge the ability of the cable and charger and weigh that against the needs of the device/battery. The speed at which your device gets charged depends on how well all those parts are matched.
Most charge rate applications show you the amount of power that is going into/out of your battery. This is a "net" number, there is usually more power going in than is displayed but it is being used up before it makes it to the battery. The charging rate (in milliamps) will go up and down as the charge controller negotiates with the other components and also because the device is doing other things in the background that take power.
As your battery filles up your device will draw less and less energy so it's normal for your charge rate readings to decrease over time. This is also why it's important to do these tests when your battery is close to empty.
For standard USB type charging the voltage should always be 5V. If you use more it could fry your device. Amps do not work that way. If you have a charger that will do 2A but your phone only needs 1A, your charge controller will only draw 1A (provided your cable can handle it).
The cheaper the charger the more likely they will overstate the amperage the charger is capable of.
Cables wear out over time and get worse at charging especially when they are flexed a lot which is normal for charging cables.
Some of the newer cables that are intended for fast charge devices are actually rated for X number of amps, this is a good thing.
There are ways to measure charge rate using hardware which is useful when your device isn't a phone or tablet but that's a whole other ball of wax.