I can't exactly answer that. But a 6 amp-hour battery isn't noticeably heavier than a 4 amp-hour battery when connected to the buffer. However, I imagine if you jumped to an 8, 9, or 12 amp-hour battery that would make a bigger difference and probably throw off the balance somewhat. Then again, I don't have any batteries larger than a 6 amp-hour. FYI, one 6 amp-hour battery will polish my entire F150 or wife's Toyota Sienna.