Arduino output voltage problem and bad shutdown (with battery)

Hi everyone, this is my first post on this forum so i hope i'm not in the wrong section but, i have a problem to solve with my Arduino UNO.

I basically need 2 things: 1)That my LCD screen works well with my Arduino (I got a Nextion HMI 2.8" Touch Display). 2)That my Arduino works well when powered from battery.

P.S. : Nextion display NEEDS at least 4.75V and 60mA from VCC pin or it can be easily damaged.

I have two 'old' powerbanks that output around 5V each, so i decided to simply use one of them to power my Arduino.

I tried this with each powerbank (They are like 2000mAh with 5V@350mAh output)

Everything works well, but then when the power bank is nearly discharged, the output voltage (from the Arduino VCC pin) goes down to around 2-3V and the Arduino starts to blink and reboot randomly, trying to power on unsuccessfully until the battery definetly goes off. (While the output of the powerbank remains 5V from the USB :confused: )

My expectations were that if the battery discharged, Arduino would turn off as soon as he did not had the minimum power required. ([u]So my Nextion LCD wouldn't be damaged[/u])

BUT if i power the Arduino using a new battery pack (This is 10000mAh and 5V@1A/2.1A output). It behaves perfectly, maintaining 5V output from VCC until the battery discharges and it shuts down (Instantly). It's like that the new powerbank automatically shuts off if it can't provide a certain amount of current..

What is the problem? It's the output current of the old powerbanks too low? Or they have a bad voltage regulation? I'm new so i'm a bit confused.. :(

Thanks in advance! P.S.: English is not my main language, so any correction is well accepted :)

You could use the Arduino to monitor the voltage from the powerbank and take some action if it fell below some threshold.

...R

I tried but the problem it's that the voltage from the powerbank is correct (From 5V to instantly 0V when it's discharged), while the VCC pin voltage from the Arduino is wrong as i said in the first post :(

Trying to monitor the VCC pin voltage of the Arduino directly from it is almost impossible because it shuts down before it can even recognise the change in the output voltage :confused:

Probably i just need a more powerful powerbank (With more mA output)?

I guess the powerbank has some form of voltage regulator to produce a steady 5v. Is it possible to monitor the actual battery voltage upstream of the regulator?

I suspect the fluctuating voltage on VCC is due to intemittent drawing of current - it falls when the powerbank can't meet the need. But then the load falls and the powerbank can meet the need again (briefly).

Another strategy might be to send the Arduino program into an endless loop at the first sign of trouble. Though that would not work if the supply voltage falls low enough to cause the Arduino to reset.

It may actually be easier to manage the situation if the Arduino was powered directly from a battery without any external voltage regulation (assuming the battery voltage is within the acceptable range for the Arduino).

If the problem is really serious you could have another "backup" battery.

...R