What activity allows to increase body battery except from sleep?

How can I increase body battery?

I know it is possible because when i am doing what i like, for example programming or reading, body battery increases but very slow.

How can i make it go faster up except from sleep?

Is there any kind of breathing or meditating excercise which could speed it up?

If my resting heart rate is 56bpm, maybe reducing it to 40bpm woold allow for it but how?