When I returned a modem I was renting from my ISP, the company didn't want back the battery backup unit that came with it. Don't let that $129 retail price fool you, these go for at best $30 on eBay. I'm not really one for selling stuff on eBay anyway, so I thought I'd come up with a little project.
The battery backup unit has an output of 3A, 12V. Taking a page from my previous 12V effort, I thought I could easily convert the 12V to a 5V USB connection and use it as a backup power supply for my wife and my phones. The battery is 7.2 Ah, so somewhat similar to this much smaller Anker battery backup. Although I don't think you can charge the Anker and my phone simultaneously off AC like my unit will do.
In addition to the Belkin battery unit, here's what I used:
12V plug socket, $6
Dual USB car charger, $8 (Although, I should have got this 3A one instead)
Heat shrink tubing, $9
Solderless wire terminal and crimping tool, $13
Here's what I did. I'm sure it isn't best practice.
First, I chopped off the output lead on the power supply. I wasn't sure which of the two wires was positive or negative so I tested them with a multimeter and labeled them.
Here's the 12V terminal. I clipped off the eye terminals after I took this photo.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgPFZ3zwmbcKOJZBiBBcugRYk8YqpJzI1W1wSKkW8W3xN7beZaSVZS4Cl_J9V7KbaUd9vg-wseYTNr4QoIH-Qkr7xTVxP7kUUqZcmhWee2dHbQtjABHuD6gDQ3BdINhBahaVp6D1SsDoQ0/s320/blogger-image--905603509.jpg)
I stripped the ends of the wires and connected the corresponding leads on the power supply and 12v terminal using the butt-couplers.
I covered the couplers with some shrink tube and added some strain relief with some cable ties.
The smart thing to do here would be to test the USB output. I wasn't sure how to do that so I plugged in an old USB device, in this case my wife's old iPhone 3 that my son plays on occasionally. He probably get's too much screen time anyway.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEix1m9UH7yv99fT6I97LFJr8Uk1PTYA_Kb-vtNJOIJF1orsEdy2zzpz444HgTNvBOCphqLGMB7d93NK4gCITFaruYIBGfT6p3_SZ_kjCNlBbKu-WhDi_ib78elBGSQZBczOVWQ3lGt9l7M/s320/blogger-image--1165312294.jpg)
Hey, it's charging! Right now the power supply is plugged into an AC outlet
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgX5_x_t-yQfriWcTi-HPnAgHPB7veARCU_wFHnLd4aTqTJSjBqq6Cl5HJnTibBm6Czd3hglmohuPC4OJWCBUOeVVmBVgW4Cd8bF9yWWLEs-kyjPDPbgUqdnXC51hoLM_SRXYf84GRtZCU/s320/blogger-image-1796110712.jpg)
In this configuration I unplugged the power supply and the iPhone is charging off the backup battery. Success!
I haven't decided where I want to put this yet. I was thinking I would hide it near my charging station and always keep the phone chargers plugged into it. In the event of a power outage, our phones would still charge up.
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