West Indies slumped to a 284-run loss in the second and final test at The Wanderers on Saturday after being bowled out in their second innings for a paltry 106 in 35.1 overs, chasing 391 for victory.
"Away from home we haven't scored enough runs. It was the same in Australia," Brathwaite said. "I still think we are making some good steps, but looking at the first Test (in Pretoria), we were in some good positions (with the bat) but we crumbled.
"We need to improve. Technically, yes we need to work on our flaws, but the mind also needs to be in the right place. It's all about the grind. We didn't score enough runs, it’s as simple as that.
"When we are on the pitch, we need to do it. We have done it before, against England at home and away. We've got to show that we are top batsmen and we haven't done that."
Brathwaite admitted to his own struggles in a series in which he scored 46 runs in four innings and lost his wicket to South African fast bowler Kagiso Rabada (27) on each occasion.
"I’m extremely disappointed, especially today," he said. "I was feeling quite good but was dismissed early (again). As a leader, I like to lead from the front, and it didn't happen this series. Next series, I've got to be better."
That next test series will be at home against India in July, but West Indies now take on South Africa in three One-Day International matches, starting in East London on Thursday, followed by a further three Twenty20 International fixtures.
