Adrian Kingsley-Hughes/

The other day, I found myself repairing someone's rather painful failed repair. 

The client had a defective Joy-Con for their child'sNintendo Switch ,andit seemed that the battery had failed.

Also: Why you need a batteryless jump starter (and how it works)

Rather than buy a new Joy-Con, they decided it would make a decent repair project andbought replacement batteries . TheseNintendo joycons  are quite easy to open and the battery easy to replace, so itisa good repair project.

The repair seemed to go well; but after refitting the battery, the Joy-Con still didn't work. It was dead and wouldn't seem to charge up, so they went back in, started poking around, and then things took a serious turn: They accidentally broke the little fastener that connects the battery to the Joy-Con.

Thisis where I came in. I assured the client that things like this happen, that the broken connector could be fixed with a bit of soldering, and that the problem with the "new" battery was that it was so completely discharged, it wouldn't charge up when connected to the Nintendo Switch.

Also: How to solder: Tools, tips, and tricks to get you started the easy way

But the underlying issue here is simple -- and quite common: You can't fully trust "new" parts to be working properly. The most common repair that people start out with is a battery swap; whenever possible, I test batteries before fitting them, because having to open something up a second time to get at the battery increases your risk of breaking something.

Batteries are easy to test: all you need is a multimeter set to read DC volts, and you touch the red lead to the red wire or the one marked as positive (+), the black lead to the black wire or the one marked as negative (-) and compare the reading on the screen to the rated voltage on the battery.

Also: The best rechargeable batteries you can buy

The Joy-Con has a single-cell lithium ion battery with a voltage of 3.7 volts. Fully charged, these hit a high of around 4.2 volts, and fully discharged can be below 3.3 volts (you can find these numbers for different batteries with a quick search of the internet). For some reason the replacement battery had drained to below 3.3 volts and so it wouldn't charge.

Testing a rechargeable battery

Adrian Kingsley-Hughes/

It's a super quick test.

I now make a habit of testing all rechargeable batteries before fitting, because I too have fitted a defective battery into a device, and was left scratching my head as to what was the matter.

Also: This $10 gadget is my favorite repair tool of all time

I have a trick up my sleeve, in the form of a littleTP4056 charging board . 

TP4056 charging board

Adrian Kingsley-Hughes/

This board is designed for charging single-cell lithium ion batteries -- you connect the battery leads to the module (I used clips), connect USB power to the module, and wait for it to charge the battery.

This brought the Joy-Con battery to full charge, and it has been working fine since.

Bringing a discharged lithium ion battery back to life with a TP4056 charging board

Adrian Kingsley-Hughes/

You can get these charging boards forUSB-C and microUSB , they're cheap -- you can buyfive for only$6 -- and they're great for charging single-cell lithium ion batteries outside of the device they're supposed to be in.

Also: You'll never guess how many tech repair tools this little bag can fit

Need a multimeter? I really like thePokit Pro that connects to a smartphone , but if you're starting out, you canpick up a good multimeter for$12 .

See also

This$30 gadget claims to add years to your phone's lifespan. Here's howThis is the USB flash drive James Bond would useHow to strip wires like a pro (and my must-have tools)Stop! Your Apple charger may be a counterfeit, and this tiny gadget can tellThis$10 gadget is my favorite repair tool of all time

• This$30 gadget claims to add years to your phone's lifespan. Here's how
• This is the USB flash drive James Bond would use
• How to strip wires like a pro (and my must-have tools)
• Stop! Your Apple charger may be a counterfeit, and this tiny gadget can tell
• This$10 gadget is my favorite repair tool of all time