What's the easiest, least intrusive way to monitor voltage, charging status, and remaining charge of a USB battery pack?
Battery packs and charging circuits for mobile projects can be complicated and expensive to design. Meanwhile, there are a ton of relatively cheap, small, high capacity Lipo battery packs with a convenient USB jack for charging and discharging. Unfortunately, they're designed for consumer uses like recharging cell phones, and not for tinkering, so there's no formal interface for getting battery status.
If you wanted to wire one of these into a microcontroller or SBC so the system could report remaining charge, is the only option to break one open, hope you don't destroy it in the process, and hope the charging circuitry is hackable?
Possible solutions I've thought of are:
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Using an ADC to directly read the voltage on the battery output, but this probably wouldn't work since the output from the battery is regulated at 5V. Even close to being dead, it'll probably still read 5V.
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Wire a coulomb counter in series with the battery. This would probably be able to track total energy charged/discharged, but it wouldn't have a reference point, so it still wouldn't be able to tell you remaining charge. Also, on batteries with multiple jacks, you'd have to have a separate counter for each output you used.
Are there any other options?
Best Answer
I'll put the links in an answer so I don't run out of room again.
I have used this one.
There is also this one
Like I said before in the comments, the first one does more than just measure voltage and then approximate the capacity. When first connected it charged the battery to 4.2 volts and shut down, but read the capacity as only 85%. On the second discharge, it read the capacity as 0% at 3.5 volts, and still allowed discharge until about 3.1 volts before it stopped the discharge. After that it got more and more accurate with each charge/discharge cycle. It is far from perfect, but more accurate now. It has problems with accuracy under about 3.5 volts as the batteries tend to be closer to empty than the pcb thinks, so it always reports abouts 30% remaining when it is closer to 20%. Other than that it seems to be OK. I doubt it is coloumb counting or I think that it would get more accurate. However, I have only done full charge/recharges maybe 5 or 6 times and after that it has been 30 or 40 partial charges/recharges.
The second link is to an interesting looking fuel guage. It measures the impedance and current of your battery pack. It differs from the first link as the first one is a charger as well and protects from over charge and over discharge and protects from short circuit. I have not yet used the fuel guage from the second link so I can't say whether it actually works as advertised.
Hope this helps.
If the ebay link is dead, I will try to find another.