What could a small peasized lump on the testicles. painless.

Get checked: If its fixed on the testicle or growing you need to get checked out quickly.

Benign if not hard: Little "ball" could be the head of your apididymis which attaches to top of testicle, or could be a small epididymal cyst. Might also be a tiny hydrocele of spermatic cord. None of which need treatment unless it becomes symptomatic. It is only hard lumps in or on testicle which might be serious, i.e. A tumor.