I guess you look online to see what the rated voltage is for the track & pump motors you're powering & don't exceed that.
The Jung pump in my Vario is running about 4000rpm (4s 16,8v @600kv, motor is 10,800rpm with a 2,5:1 belt reduction), and I only rev it to the max (or near it) on boom lift. Stick, bucket & boom down is 1/2 to 2/3's of that
Other guys are running their Vario hoes with 3s... that's a bit slow for me.
Thanx for the pic... what's the LxWxH, plz?