Unlimited USB External Battery Pack




Introduction: Unlimited USB External Battery Pack

Smartphones are notorious energy hogs. To combat this there are several manufactures that offer aftermarket replacements of up to 3,500 mAh (3.5 amps).

Online you can get 2 batteries and a wall charger for about $20 but all they’re good for is the specific phone they were purchased for.

With so many devices using USB charging ports (5 vdc) it’s a shame to throw these away when you switch devices.

Here’s a solution for an external battery pack that will charge / run any USB device(s) from either battries or a Solar Charger


1. Web acquired charger and 2 batteries ($20) – Make sure charger has spring pins so hooks will fit. May need to file case if not.
2. 5 vdc USB re-chargeable battery ($10) – used as circuit breaker / thermal overload / conditioner between pack and device. Would rather lose battery than phone, MP3 Player, or tablet if there is a malfunction.
3. 2 USB charging cords – 1 for inline battery if required and 1 for device
4. 1 set “J” hook test leads ($4) Radio Shack
5. Solar Panel ($12 Harbor Freight - comes with removale 2 AA battries)

USB assembly

1. Cut old USB cord - save ends – female for external pack , male for Solar Charger
2. Strip Red & Black wires about 1” (cut off white and green)
3. Wrap / solder / tape red to red test lead and black to black.

The red is + and black is -.


1. Place full 3,500 mAh battery in charger
2. Hook red “J” hook test lead to positive charging pin,
3. Hook black “J” hook to negative pin.
4. Connect in line protection battery
5. Connect device

I have a total of almost 18,000 mAh in rechargeable batteries – (3) 3,500’s, (2) 500’s, 1,000, also (8) AA, and (8) AAA in quad holders.

Can use Solar Charger to charge batteries or device by hooking the male end wires to alligator leads, red to red / black to black. Make sure to insulate wires to prevent short.

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    Reply 10 years ago on Introduction

    2 battries shown - primary one is 3500mAh from EBay (2 battries w/ charger for HTC EVO smartphone $20) the smaller is a 500 mAh by Lenmar ($5 Bed Bath & Beyonf on sale) have 3 of the coil cords now - NOT good for data - only 2 wires with interchagable ends.

    Advise using intermediate cheap battery to act as circuit breaker / over temp potection.