BELOMI Battery Monitor, Waterproof Battery Capacity Indicator with Alarm, Lead Acid and Lithium Ion Voltage Monitor Indicator, 8-100V Voltage Monitor Capacity Percentage Tester (Multicolour)

I think the product is fine and will perform its job as a simple battery monitor for various common battery technologies. If you too, happen to see colors displayed in the product images on the Amazon website, this must be some sort of issue with your eyes / brains / PC monitor setting, or more likely an issue related to less then accurate advertisement of a product, as this battery monitor is certainly not capable of rendering color per LCD. There is some attempt made on the amazon product page to offer some sort of set-up instructions - those are incomplete in parts and inaccurate in some other sections. Since similar products are offered here and per other vendors, it may be best to apply those instructions instead.

This works good but does require setup.

The hardware is decent, especially for the price. Voltage is ~0.1V off at 40V. Unlike other similar units, this one doesn't appear to have a calibration function. Power consumption is 13mA when the unit is on, and 0 mA when switched off with the power button.Unit comes with no instructions, but the menu (accessed by long pressing the settings button) is somewhat intuitive. Settings 1-3 are for configuring the battery type and number of cells. Setting 5 is for enabling the power-off timeout. I can't figure out what settings 7 and 4 do.The biggest flaw is that this unit has poor firmware. Specifically, when computing battery percentages for Lithium and Lithium Iron batteries, the unit assumes that the state of charge is linear with voltage (e.g. if 42V is 100% and 30V is 0%, then 36V is 50%). However, the SoC curves for most batteries are not straight lines, and for a 12S LiFePo4 battery 36V is only 10% of remaining charge, not 50%. This makes the battery percentage feature useless.There are similar looking devices on Amazon that appear to have better firmware (based on reviews). I recommend getting one of those instead.UPDATE: I found a workaround for incorrect battery percentage. In settings, page 4 allows you to enter the 0% and 100% voltage levels manually (bottom button to change the current digit, press and hold the bottom button to move to the next digit). While SoC curves are not linear for Lithium batteries overall, they are pretty linear from 90% to 20% or so. So if you choose the 0% and 100% values such that the 90% and 20% values match the expected values, the battery percentage indicator is quite usable.I bought a second unit and added a star to the rating.