I would like to check the health of some large capacity (circa 10,000mAh) 5V USB battery packs that have been sitting around for a long time. There is another post "How to monitor voltage and charge status in USB battery pack" but this didn't say when to discard a pack.

How come they're 5V when LIPOs are 3.7V? i.e. is it 2S with buck converter or 1S with boost converter?

I looked at a Skyrc S60 balance charger which can measure resistance and other things on drone Lipo batteries but these seem to have balance connector leads. So I can't see how to connect a 5V retail battery pack with female micro-USB charging socket and normal female USB supply sockets.

I think the balance charger is for drone batteries and so may be unsuited to check health of retail 5V battery packs. As I understand it such battery packs have extra circuits to make them safe e.g. prevent overcharging. Presumably that makes it harder to measure resistance etc. Am I correct? Is it worth me buying a S60 for this?

So I'd like to find a way to check health of battery pack - ideally other than waiting to see if case starts blowing larger due to gases from deterioration (eg spinning case to see if cases have caused case to curve out). Would a low output voltage be such an indication e.g. if I only got 4.5V then it's time to chuck?

If the battery pack is ok then can I charge and draw power from it at the same time i.e. as an uninterruptible power supply? I have a pi zero that I'd like to power from a LIPO connected to a large solar cell.

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    \$\begingroup\$ There is certainly a converter inside the pack. What does the manufacturers documentation say about the amount of cells inside the battery pack? 3V under load is the lowest these cells should ever go. \$\endgroup\$ – kva May 29 '17 at 14:00
  • \$\begingroup\$ Some chemistries have an absolute minimum of 2.5V per cell, although it's not recommended to discharge them that deeply regularly. \$\endgroup\$ – Dampmaskin May 29 '17 at 14:25
  • \$\begingroup\$ This sounds like a usage question. Charge your pack fully and see whether it works after that. If it doesn't charge or discharges in 10 minutes, buy a new one. \$\endgroup\$ – Dmitry Grigoryev Jun 6 '17 at 9:24

Most commonly used electronics for 5V USB battery packs are quite similar.

Of course inside there is a charger that uses 5V input to charge the batteries with constant current. Charging stops when batteries reach 4.15.-4.25V depending on model.

Also there is a boost regultator which boosts battery voltage (2.5V to 4.25V) to 5V on USB output plug. Discharging also is controlled and stops at a certain voltage but is this voltage (3.00, 2.75, 2.50) correctly matched with battery specs one can only hope if the bank is "no name" brand.

I doubt you can measure this correct with a device like SkyRC S60 that is designed to work with raw battery cells.

Measuring voltage - most of these battery banks even being cheap have something "smart" in them. When there is no load attached (when load current is neglectably small) average output voltage is less than 5V and output LED is turned off. This is done to minimize self discharge of the system. So measuring 4.5V may be normal in this state and it doesn't mean weak battery.

How to measure bank's capacity? Charge up the bank for long enough period - like 24h, then connect a constant load and measure how much time it will take to turn off. You can connect a 10ohm/5W resistor for 0.5A load current and start waiting. If the pack is really 10'000mAh time would be about 14-15h. You can try with smaller ressitor (for example 4x10ohm/5W in parallel) to discharge with 2A on the USB but this may be too much for the bank's electronics and even if it handles this current, it will discharge your cells faster and you will get wrong reading.

I think the battery bank will lower its output voltage only on current overload, but not when its cells are empty. On discharged cells the bank would stop and its output will be 0.

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