Motherboard battery removed, can't boot up anymore

Hello everyone,
I am facing something similar - I press the power button on the teach pendant and it shows the logo then turns off. Our model is UR5/CB 3.0. I took the pendant apart (see images), there was no battery installed -I guess it is 3.0 version, that’s why. What should I do to fix this issue since I cannot replace the battery in this case?

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