Powering Pi Zero and 4 inch display with a battery

[Poi123]

Hello,

I have been working on a DIY portable game device using a Pi Zero W and this display https://www.waveshare.com/wiki/4inch_HDMI_LCD

Initially I tried out powering everything with a a regular 2200 mAh power bank with an output of 5.0V / 1000mA. Just to see if it would work with a small power source. I just connected the power bank into the USB port of the Pi and everything worked properly, and for an acceptable amount of time too!

Later I decided I wanted to see an estimate on the amount of power left on the battery, so I got this battery pack https://www.adafruit.com/product/354 this fuel guage https://www.adafruit.com/product/5580 and the Power Boost 1000C.

I connected the battery pack to the fuel guage, the fuel guage to the power boost and finally the power boost to the Pi, and... it almost works.

I say almost because I think the display is just too power hungry in this setup. Eventually I figured that if I turn the backlight of the display off before powering the Pi, and then I turn it on, somehow everything manages to continue working properly afterwards. Seems like the Pi just needs all the power for itself initially and then it's ok with the display hogging everything.

It's not terrible, but I would rather have the whole thing turn on with just the one switch, rather than making sure the display is off, then turning the main power on and then turning the display on.

Is there a different way I could power all of this stuff? I was thinking of getting a slightly smaller display, I am sure that would help a lot.

But maybe there is something else I could try. I have read elsewhere that Lipo batteries provide more power than Lion, is this true? Originally I went with the Lion pack just because I liked how it looked and from looking at the specs they seemed to be the same as Lipo, but maybe they are not exactly the same?

Any ideas would help. I don't even know how much power the whole thing is consuming and am not sure how to get that information, reading a little bit sounds like it's not that easy to find out exactly how much energy a project is using.

[adafruit_support_mike]

Check with Waveshare to see if the display has a logical backlight control as well as the manual switch.

If so, you should be able to control the backlight from one of the RasPi's GPIO pins. The display logic will work normally when the RasPi boots, but you won't see anything on the screen. Then once the RasPi is done with its boot process, it can set the appropriate GPIO pin and turn on the backlight automatically.

That does assume the existence of a backlight control pin on the display though.

[Poi123]

After reading the wiki about my display more carefully, it does seem to be possible to control the backlight with a GPIO pin, the problem is that I don't know if I can do the soldering properly, it's so tiny!

On top of that, it looks like there is already a component in the pad you are supposed to solder a cable to, but again, it's so tiny I can't even see what it is.