What is the "BTY VOLT" on AC side?

Q: What the volt adjustment is for on the battery charger it the small white round switch with #o to 9 so please what dose it do?
A: On the volt adjustment, you can adjust this to match your battery voltage, "1" is the lowest battery voltage, and "8" is the highest battery voltage,(0 and 9 do not have charging function), you can begin from 1, then 2, then 3..., until the right number that suit for your battery voltage.