What's killing my power packs?

Projects General Guidance
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I have a robot project with 12V and 5V power needs. I have used USB 'power banks' for the 5V need. These are the type used to charge phones, 2600 or 5200 mAh capacity, I believe they have 18650 batteries inside. Unfortunately 2 of the power banks have been damaged such that they no longer charge. I would like to get opinions on the situation as I do not wish to ruin more batteries. The robot currently has high power leds that run on a large 100Wh 12V Li-ion battery; 5V power banks power a servo, an IR sensor, and an mp3 player.

I found recently from scoping the sensor signal it was very noisy @50Hz when the servo was running, so I tried a separate battery for the servo. I also tied the battery grounds together. This removed a lot of noise on the sensor output, as did adding a RC LPF circuit on the sensor output. Strangely when I added a 100uF capacitor across servo power the noise amplitude increased (resonant circuit??) significantly on the IR sensor output, at least doubled. I also tried using the separate 5v battery on the sensor instead, but the 50Hz noise remained prominent. All the devices are within about 1-2ft of each other, the longest wire is ~1.5ft long. In this testing work of a period of a few days I used 3 batteries and 2 of them no longer charge and I was wondering what can I do to prevent this battery damage. Is this a common problem with this type of battery and how could I avoid or improve the situation. Thanks.

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Run-of-the-mill 18650 batteries will die if discharged below 2.5V-2.75V

Perhaps your power pack is not protecting the batteries, or the batteries themselves are not protected against over discharging.

https://skygenius.cc/blogs/guides/beginners-guide-18650-battery

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Servo SG-90 requires a 50Hz PWM signal to work which is being generated by the Arduino.

Posting a diagram showing all electrical connections of your project will get you more help, faster. A hand-drawn one will do

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These device must have switching regulators in them to ensure the correct voltage for phone charging. You are drawing way too much current from the circuit. You can only draw the amount necessary to charge your phone battery. Is there no documentation for the devices that show the maximum current available from the charging port?

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Yes they have ratings printed on them. The ones that died say 5V, 1A. The one that survived says 2.1A although it did quit for a while. I don't think the servo is that heavily loaded but I'll try to measure current. The mp3 player and IR sensor don't take much. The batteries get hot now when I put them on charge but don't charge. I found a 3A Schottky diode to try because I thought maybe inductive back EMF or something got them.

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