I am getting a new tablet soonish, and we don’t have the best power where I live, the worst of it comes maybe once or twice a year where power is down for 12+ hours. currently my tablet doesnt have the space on it to hold media, it kills sd cards, and with no power means no internet for me so while a power bank would keep it going longer, what’s the point? my new one though has half a tb built in, so now keeping it going in power outs kind of became something I want to do.
Now, I could go with a name brand, take a 5000mah and spend 50$ on it, but i’m kind of willing to roll dice on something with more mah that other people have found ‘reliable’. this isn’t going to be an everyday thing, this is likely going to be a 5x a year thing and probably not needed for more than 1 of those events. I just want to make sure it gets me though said event.
I bought XIAOMI Mi Power Bank 3 Ultra 10000mAh (Rated capacity 5500 mAh (5V/3A)) for $19,54 over a month ago and it’s ok.
It does what it’s supposed to do. Although it has its limits… it will turn off if the current consumption is low for example 80mA, which is quite typical for power banks supposedly. However, it has a low voltage charging mode for 2H.
5500mAh actually usable capacity of advertised 10000mAh? Just curious if this is typical of today’s power banks. I haven’t used one for a long long time…
Re-reading my own replies and thought it through again. I believe I made the wrong interpretation.
So in Tim’s post. The Xiaomi’s actual usable capacity should be: 5500 x 5/(10000 x 3.7) ==> about 75% usable. In your power bank, it’s about 80% usable.
Somewhere between 80% to 90% or above usable capacity is what I would expect. So it’s about right.
Consider buying a cheap UPS with 12V SLA battery, leaving it powered off (no AC output), and wiring a car USB charger to the battery. The smallest/cheapest would provide nearly 12000mAH, though a little over your budget. For a bit more money, you could even double that capacity. You might also be able to power your modem/router (if 5V or 12V) and keep your internet up and running as well. See:
Probably everything in this price range has such parameters. This is about discharging at 5V/3A, and when you have less then…
People often buy cheap versions with a large capacity, which is largely a PR procedure, and then they wonder why this power bank works so poorly for them.
Humans and battery chemistry don’t mix well. Most lithium battery capacity ratings are for 0.2C or a discharge rate of 20%. The further you get from that the more it changes, and it isn’t linear. Of course most people want to go full throttle with ‘all the things’ and if they gave batteries a capacity rating reflecting how it works when abused, someone else would simply come along and give a rating people want to believe in, regardless of reality.
I did something similar to above, but used a panel mount USB charger made for 12V nominal input and got old but unused 4S3P battery packs with BMS for $8 plus shipping. It works great and I plan on mounting it to my electric bike to power lights and charge my phone.
Out of curiosity, I did some digging on Xiaomi power banks. More on this at the end.
My last power bank was a ‘dumb’ 7000mAh Sony CycleEnergy. It had a usable capacity close to 90% of advertised. That was like more than 10 years ago. It costed more than 5 times of a ‘dumber’ version of Xiaomi’s recent-year 10000mAh issues. I think Chinese brands really have democratized Lithium ion power banks!
I still have the Sony CycleEnergy but the battery cell is obviously dead. I kept it for the shell and charging/discharging circuit board. Also in the likelihood that I might need a power bank, then I’m going to revive it with a brand new quality Japanese/Korean/Chinese battery cells. The need never comes as smartphone battery life improves a lot in recent years.
From my digging, the latest Xiaomi ‘smart’ 10000mAh Pro power bank has a usable capacity up to about 94.5% (i.e. 7000 mAh output tested at 5V 1A discharging condition). Not bad at all. For its price, it’s a decent and wise choice.
I’m out of the loop, what happened? Looking online, it looks like some anker eufy cameras stored video in AWS without users consent. I think that is a given at this point, unless you get devices that work offline, you are almost guaranteed data is going to be exfiltrated through them (either by the company itself, or by script kiddies finding the cameras and exploiting their obviously present security vulnerabilities).
I like the anker and aukey chargers and power banks. I only bought their chargers, but was considering maybe buying one of the anker usb charger / power bank brick combo, if I can find details if those can function as a mini UPS (that would be sick).
For myself, I have a trash Kit: Fresh power bank I literally found in the recycle bin (it was just its USB cable that was bad, the bank is still charging my phone around one time while in heavy use). And I bought myself a Skull Candy power bank (had some gift cards for barnse and noble, had to spend them somehow).
I kinda want one of the anker powerbank / charger combo, because I can power both my pi and my portable monitor with one brick, which I could theoretically unplug and be on the go with.
Wait, so you lose almost half the energy stored in the battery when discharging rapidly?
Is there a rough average curve to work from?
There are warnings in this thread about 3 A being the realm of exponential losses, but is 2 A? Are the mAh ratings roughly true for 1 A power draw?
Does this change with the capacity? Is 2 A draw for a larger battery equivalent in percentage loss to 1 A draw on a smaller battery with smaller or fewer cells?
Yes. Drawing 2A from a 2Ah (2000mAh) battery is not the same as drawing 2A from a bank of 10 of those batteries totaling 20Ah. You would have to double check on the cell specs, and age plus wear factor in, but if the rating for the cells is at 0.2C (C stands for the rated capacity), then you won’t get a full hour with 2A draw (1C), but would get more than 10 hours from the bank of 10 (0.1C).
This also affects lifespan, though it is my understanding (within reason) that heat caused by drawing a bit more or a bit less current isn’t nearly as detrimental as drawing the battery all the way to 0% and charging to 100% regularly. For instance, if you limit it between 30% and 80%, you cut the usable capacity by half, but the cells will last 7 times as long. This means over the life of the battery you will be able to draw 3.5 times as much energy.
In my case, I usually try to keep all my packs within the 30% to 80% range, but on the occasion I need the extra capacity I just use it and don’t worry. If I do it infrequently then I’m probably getting around 3 times or more lifespan than someone who goes from full til dead every time. That coupled with low price, quality cells gives me really great value for my ebikes. It also allows me to afford a much larger pack so I can get around on most days only using the middle half of the capacity. Buying a prebuilt pack of that size with quality cells would cost more than I paid for the whole bike. Then again, I paid a great deal of time learning all of this.
