Connection of battery and ECUs?

Hello dear elk friends, I have a technical question: What connection is there between the battery and the control units or the vehicle technology? I have always assumed that the battery is “only” to start; but what should not be the case due to my following description. I had for some time the problem, which somehow the moose did not want to do so properly. Feeled power had been missing, he has delayed in giving gas (as if the command “Gib” Then the throttle cap was added, but only when starting and it went out again after some time. The engine also didn’t start immediately, or occasionally went out immediately again. Long speech short sense, it was the battery. That was over. New pure everything again good!! But what does the battery have to do with the throttle flap when starting? Please close my car education gap. Greetings Hessenelch