Can't Get Battery Pack to Charge with 20W Brick and USB-C to USB-A Cable

Thanks for your help, in advance.

I use a 6,000mW battery to power my Oticon More3 charger, which lives in a drawer in my night table. It takes forever to charge using a 5W brick, and charges a bit faster using a 12W brick and USB-A to Lightning connector.

I have a 20W brick (USB-C only) to charge our IPhones and iPad, which works fine for the devices.

Wanting to access the higher wattage charger to speed up my battery charging, I bought a USB-C to USB-A cable, but none of my external batteries will charge when connected to the 20W wall charger.

Is this because the batteries can’t handle the higher wattage? (I thought the batteries would only draw what it could take from the higher wattage brick.)

Would someone please advise as to what’s going on?

[Is there a solution, or do I have to return the cable I bought?]

C-A cable, are you sure the cable works? It should but you never know.

The wattage isn’t an issue. It’s no doubt a bad cable.

If you are talking about a battery backup charger, then what a happening is the hearing aids aren’t drawing enough current to keep the backup battery from shutting down, and as soon as the power is off of the hearing aid charger the aids power on and are discharging the battery in the aids. I had found the same issue with my OPNS1 rechargeable aids. The best thing is to just use the charger and power adapter that came with the aids.

@cvkemp: That’s not the issue, Chuck. The aids charge fine from the battery. I’m trying to charge the battery from the wall.

Thanks for replying, anyway.

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Ok sorry about that. I have a few backup battery chargers, due to camping and sometimes be off the grid totally. I have one that got just for m hearing aid charger that never powers down when the current goes below a threshold, otherwise the hearing aid charger loses it power and the aids power on

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@roybrocklebank and @oetbyg: I have tried the cord with all my batteries. None of them will charge with that cable.

If it’s not a wattage/electronics issue, I will exchange it for a new cord and try again.

Thanks for your replies.

@cvkemp: Yes, I know what you mean. None of my 3 batteries shuts down. The two smaller ones don’t take long to charge on a 5W brick, but the big fella takes forever.

MrsSpud’s 12W charger is a bit quicker, but I was really hoping that I could take advantage of the 20W charger (Apple - approved for iPhone SE 2 and IPad Air 3) to charge the 6000 mW battery in 3 or 4 hours, versus 12.

But I appreciate your help: thank you, Chuck.

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Does seem like you’ve confirmed that the cable is bad. However, even with good cable there is no guarantee that the 20W device will be able to charge up your battery any quicker than the 12 device.

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USB-C devices negotiate power. For example, the 20 Watt USB-C power adapter for my iPad will supply 5 Volts at up to 3 amps and 9 Volts at up to 2.22 amps. The USB-C power adapter for my MacBook Pro will supply 20.2 Volts at up to 4.3 amps, 9 volts at up to 3 amps, and 5.2 volts at 2.4 amps. The cables must support negotiation and the maximum current to be supplied. Early on, many USB-C cables didn’t meet specs and didn’t operate correctly for either power delivery or data. That is probably still true so you need to ensure that any USB-C cable (or adapter or device) actually meets specifications and is appropriate for your intended use. Cables certified to USB-IF (Implementers Forum) for the intended purpose will probably work. That said, all devices (charger, cable, and battery in your case) must implement the desired modes to work together correctly.


@biggar and @MDB: Thanks for trying to educate me! I’m afraid that I understand little of the complexities of electronics, including USB power.

That said, I’m getting the distinct impression that my assumption that more charger wattage equals a quicker charge is wrong.

The cable is probably bad, or not engineered for my charging application, but I won’t waste my time on it: I will sneak MrsSpudGunner’s 12 watt charger into the kitchen and charge up the “BigFella” every Monday, as I’ve been doing the past month.

I’m like @cvkemp - retired - so, what’s longer charging time to a goat?

Thanks very much for your helpful replies! I appreciate it!

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What you might find useful is to get a USB digital multimeter. They are very inexpensive on Amazon and the one that I got seems to work very well. $19 at the time. I’ve checked it against my regular digital multimeters and the USB one is pretty accurate. *** (see added note at very end)

The USB device records and remember the readings, even when powered off. Since it’s probably writing to some electronic memory, it’s going to wear out eventually but it’s great while it lasts. The instructions aren’t so great and it’s a little kludgy to use (read the Amazon reviews) - plenty of other models on Amazon, too, to choose from.

It’s very useful just to tell if any current is flowing to your device. I have a 2015 device where the micro-USB contact is wearing out and if I don’t seat the charging cable properly, the device may not charge. Interfacing the USB meter in the current path makes it easy to tell in plugging in cables whether current is flowing. Similarly good for testing cables and AC adapters for USB to make sure they are delivering the voltage and amperage promised, etc.

Also, if you have a USB-powered battery pack that has no LED charge indicators and you know what the device’s capacity is and want to charge up the Li-ion battery to about 50% capacity for long-term storage (better for long-term battery lifespan than to store 100% charged), the digital USB multimeter is very helpful. I learned an important thing to keep in mind, though. Battery capacity of a Li-ion battery in terms of mAh is usually calculated in terms of delivering current at 3.7 volts (the average voltage of a single Li-ion cell during its discharge cycle). But when you are charging, you are delivering USB current at 5 Volts. What’s important in determining how much energy goes into a battery is not Volts or amps separately but the combination, Volts times amps = Watts, units of energy delivered per second.

So if your battery is rated at 2,000 mAh capacity discharging at 3.7 V average and you want to charge it to the equivalent of 50% capacity at 3.7 V (1,000 mAh), when charging at 5 V, you only need to put in 3.7/5.0 x 1,000 mAh or 740 mAh at 5 Volts input.

The check is 740 mAh x 5 Volts = 3,700 mWh (or 3.7 Wh) and so is 1,000 mAh x 3.7 Volts (3,700 mWh or 3.7 Wh). The same amount of energy was put in at 5 Volts that’s going to be taken out at 3.7 V average in discharging the Li-ion battery.

After the Texas power outage on Valentine’s Day, 2021, I bought a “25,000 mAh” battery pack. To see if I got my money’s worth, after I almost completely discharged the battery pack, I charged it back up at 5 volts and had to use the above relationships to see, Yep, the battery pack was as advertised. It took ~18,500 mAh at 5 Volts to charge the device up to 100% capacity as the 25,000 mAh rating was for ~3.7 Volts average discharge voltage.

*** (Added Note) One thing about the device that I got. At the time that I got it, it didn’t handle the highest level of fast charging (it can handle lower levels). And to handle the lower levels, you have to insert a little metal adapter into the main body of the device to accommodate the reading of increased power levels. So if your goal is to see how high-level fast charging is working for any device, e.g., iPad Pro, laptop, etc., be sure to check the specs on whatever USB digital multi-meter device that you might be interested in - mean this as a general admonition to anyone reading this post down the line - not advice to anyone in particular.


I found interesting the comment about a micro USB contact wearing out. I may have something similar happening with a USB-C contact as on rare occasion it doesn’t charge. Interestingly, even though it isn’t charging, the “lightning bolt” charge indicator shows up. Curious if that was the case for you and if you have any explanation or “stories.” (“Stories” is not intended as pejorative. It is a term I use for plausible explanations that help me make sense of things, but that I don’t really have any evidence for.)

@MDB: I understand what you mean by “stories” … trouble is that I have none.

The 20W Apple charger is only 2 weeks old, and charges our iPad and iPhones flawlessly.

The contacts on my battery packs (both USB-A and micro USB) are not worn, and they charge fine using the 5W or 12W chargers and USB-A -> micro USB cables.

I don’t know what the issue is with the USB-C -> USB-A Insignia cable is. However, if the 6000mW battery won’t charge appreciably faster on the 20W charger, I am not going to bother. I may simply return the cable and buy another 12W charger.

Thanks for helping … I sincerely appreciate it.

It can be this cause:

Thanks, but the problem has nothing to do with the iPhone.

A guess is that the 6000 mW battery expects only a 5 Volt source to charge and negotiates that. The 20 Watt charger only supplies up to 20 watts when it negotiates a 9 Volt connection (9 * 2.22) and only 15 Watts (5 * 3) when it negotiates a 5 Volt connection.

THAT’s IT, Stuart @biggar. I understand what you’re saying!

So … the BigFella can probably negotiate something with the 12W charger, and charge faster than the 5W block charger? Or is the quicker charge time a figment of my imagination?

[Thanks for your instructive input.]

My reply was actualy to Jim Lewis. Forum has irksome (to me anyway) habit of not indicating who reply is to if the reply follows immediately afterwards. Anyway. My “stories” for your situation are 1)It sounds like a bad cable, possibly with some internal discontinuity (broken wire or short) 2) Higher watt charging needs the capability to be on both ends. My best guess is that when using your 12W charger that it’s really charging your device at 10W and it would be the same with the 20W charger. My impression is that a lot of older “stuff” will take 10 watts, but I have zipp evidence for that as a bit of research shows that only Quallcom’s Quick Charge 1.0 supports that standard. Does the device you’re trying to charge have a label on it that tells what charging standard it supports? (They often require a magnifying glass or very good eyes to read)

Your battery probably negotiates a higher charge rate (current) with the larger capacity charger and that would result in a shorter charge time. However, many chargers taper down the charge current into a battery as it nears full charge so time to full charge is hard to compute. And you may have higher voltage losses in marginal cables at higher currents and that could change charge performance. Some modern notebooks that use USB-C for charging accept up to 100 watts (5 amps at 20 volts) so the cable needs to provide 5 amps with minimal voltage drop - not all USB-C cables can do that.

If you want some reading to put you to sleep, try this (and find the Compatibility issues section near the end): Wikipedia on USB-C