meter

const data = [
  {
    id: "1",
    name: "Battery A",
    intervals: [
      {
        timestamp: 1635757200,
        kwh: 20
      },
      {
        timestamp: 1635758100,
        kwh: 30
      },
      {
        timestamp: 1635759000,
        kwh: 35
      },
      {
        timestamp: 1635759900,
        kwh: 37
      },
      {
        timestamp: 1635760800,
        kwh: 38
      },
      {
        timestamp: 1635761700,
        kwh: 45
      },
      {
        timestamp: 1635762600,
        kwh: 52
      },
      {
        timestamp: 1635763500,
        kwh: 55
      },
      {
        timestamp: 1635764400,
        kwh: 60
      },
      {
        timestamp: 1635765300,
        kwh: 65
      }
    ]
  }]
  
  let y =      {
        timestamp: 1635765300,
        kwh: 75
      }
  
  let result = data.map(a => a.intervals);

let z = data[0]['intervals'].concat(y)
let a = [...data, data[0]['intervals'].y]

console.log(a)