It seems like you're facing some difficulties with testing your battery and power adapter using a multimeter. Let's go through the steps to test them properly.
To test the power adapter, you'll need to check its voltage output. Here's how you can do it:
# Set your multimeter to the DC voltage setting. Choose a range higher than the expected voltage output of your power adapter.
# Connect the positive (red) probe of the multimeter to the center pin of the power adapter's output connector.
# Connect the negative (black) probe to the outer metal shield of the power adapter's output connector.
# Turn on the power adapter and observe the multimeter reading. It should match the voltage specified on the adapter label. If the reading is significantly different or shows no voltage, the adapter may be malfunctioning.
Regarding testing the battery, you need to be cautious to avoid any damage. Follow these steps:
# Set your multimeter to the DC voltage setting, similar to the power adapter test.
# Identify the positive (+) and negative (-) terminals of the battery connector.
# Connect the positive probe of the multimeter to the positive terminal and the negative probe to the negative terminal of the battery.
# Observe the multimeter reading. If the battery is functional, it should display a voltage within the expected range for that specific battery model. If the reading is extremely low or zero, the battery might be faulty or discharged.
In case both the power adapter and battery test fine, you may want to consider checking other components or potential mistakes made during the installation of the boards. I have published daily blogs related to a multimeter on [link|https://multimeter101.com/|my website|new_window=true]. You can check it.