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  Convert Li-Battery "Power Bank" to User-supplied Cells? 
 Date Written 
john albrich Jul 17, 2014, 12:36pm EDT Report Abuse
Re: "typical" tablet/phone "backup/power-bank" conversion to USER-supplied Batteries

Has anyone here tried replacing the 3.7V Lithium cell with either 3xAA NiMH cells (maybe 4xAA NiMH cells) or 3xAA alkaline cells? If so, I'd like to know the results to save time and money.

I'm NOT interested in recharging either the NiMH or alkaline cells while they are in the "power bank"...It's OUTPUT ONLY I'm interested different battery charging issues aren't a factor.

All I want to do is try using a cheap $10-$20 "power bank" circuit to create a stable 5VDC 1A to 2A output using either ~3.7V(3xAA NiMH) or ~4.8V(3xAA alkaline) or ~5V(4xNiMH) cells. (Yes, I could design and make my own circuit to do this using components from Digi-key, but with my medical problems these days, having something with a case, connectors, etc already put together makes things a lot easier).

But, if someone has already done this I'd like to know the results.
For example, did 3xAA alkaline cells at ~4.8VDC damage the power bank DC/DC circuit? Does it run hot? Can these DC-to-DC regulators take that kind of input voltage variation or are they strictly limited to the 3.7V input of a Lithium cell?

One example, I'd like to replace the 3.7V lithium cell in a $20 "power bank"
with either NiMH cells (~3.7VDC/3xAA or ~5VDC/4xAA) or alkaline cells (~4.8VDC/3xAA new cells)

The REASON for doing this is I have selected or designed my camping equipment so that everything predominantly uses AA cells. This simplifies things a lot as I don't have to worry about carrying around, testing, storing, etc different battery types, and in a pinch I can swap "good" batteries from one device to power another device in which the batteries had been depleted. And AA cells are available just about everywhere. Thus, I'd like my "power bank" to be able to also use AA cells.

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john albrich Jul 29, 2014, 06:38am EDT Report Abuse
>> POSSIBLE Candidate for User-Replaceable Cells

On test bench, at moderate 1Amp 5V constant current draw, it provided nowhere near the claimed 20,000mAh. It provided about 4,000mAh at the 1A current drain. Clearly, they were were either:
1) very liberal in their testing methodology (unfortunately, not uncommon in producing high mAh battery claims)...or
2) they lied...or
3) it's "defective"

Given the ultra-generic labeling I discuss below, I suspect this is just for all practical purposes a low-ampacity "power bank" being marketed as high-ampacity power bank.

Leaving the rest of the post for background info as a cautionary tale for others.

One manufacturer MAY be going in the right direction...

I don't have this unit yet, so I do NOT yet know if the "built-in high-capacity" 18650 cells are user-replaceable. I'm a bit concerned about the use of the word built-in, which suggests they are soldered or welded in. Also, 20,000mAh is a LOT of energy in a small package if something goes wrong.

I plan to buy one at a currently very discounted price and will report back.
SmackTom Premium Dual USB Port External Battery Power Bank 20000mAh
-Built-in 6*18650 high capacity rechargeable Li-Ion battery, Powerful with long operation time
-Two USB output interface: 1.0A interface and 2.1A interface. Charging two your devices synchronously
-With High output LED flashlight function (quickly press the button twice, it will turn on; then quick press the button twice, it will turn off)
-Leakage protection, and five heavy security protection, very safe to use
-Safe and reliable, perfect for using on travelling and outdoor activities
Brand: Generic
Part Number: CH-BL-0062
Manuf.Part Number: CH-BL-0062

Dimensions are:
Case : ~ 5.9"L x 3.1"W x 0.9"H
Cable: ~ 20" long

edit 201407291130uct
BTW, it looks like 3000mAh 18650 cells (that include internal protection circuitry) sell for about US$9ea/qty6. Cells with no protection seem to be about US$4ea. So IF the cells are decent this may still be a good deal at the current promo price of $15 even if the unit's performance disappoints. I can certainly use 18650 cells in high-power LED flashlights and home-brew projects, and I can always use another USB2.x-standardA to USB2.x-microB cable.

Also keep in mind that such a high ampacity (20,000mAh) power bank will take a very long time to charge compared to most power banks in this price range. Heating-up while charging may also be an issue so definitely want to be sure it has plenty of air circulation during charging and use.

Edit 201407291640uct
Note: 6 x Panasonic NCR18650B Super Max 3.7V 3400mAh ==> 20,400mAh, which is closer to the power bank's claimed 20,000mAh. From what I could find out "unprotected" versions appear to cost about $9 to $10 each. Versions that claimed internal "protection" circuitry were selling for about $13each.

Edit 201408060500uct
I got the "power bank" referred to in the links

Manufacturing quality surprisingly seems decent for the price. However...
It doesn't even come marked with the manufacturer's name, product name, or model number on it, so there's no way to confirm it's even what I ordered (why I've edited to put a "strike mark" thru the links). It's like some GENERIC device. There's no way to associate/verify the claimed safety certifications label with the device...make of that what you will. The "manual" it came with (poor comprehension aside) also didn't include the mAh or refer to a specific manufacturer name, or even the model number. The manual is so generalized it could be packed with just about ANY arbitrary "power bank". In short, it could be sold as "product a", "product b", etc. and there would be no way for the customer to confirm it. The device is not designed to be opened by the consumer so the cells are not consumer-replaceable/swappable without destroying the case. Other than those observations, it does seem to work, and so far on a single charge-up, has re-charged several (approx) 50% discharged (1,000mAh plus) phones and tablets, and even topped-off an (approx) 50% discharged 5,000mAh "power bank" without a problem.

When it was delivered it was showing 2 of 4 LEDs charge then took a 1/2 day to fully charge on a 5Amp, 5VDC source, so it indeed could be high-ampacity (or just charges slowly for no particular reason).

Importantly, the manual claims the INPUT charging voltage can range from 4.5V to 20V, and using such a higher input voltage/amperage source (e.g. a car's 12V outlet) might yield much faster re-charging. Heat during charging might be a problem at elevated source voltages, but it claims to have built-in charging regulation/protection.

Input actual measured dimensions of case and cable



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