4electros said:
but the weakest battery is new, i bought it few months ago but i haven't used it until this project, so i'm surprised for that weakness, what should i do now?
Duh! My Energizer alkaline 9V batteries are stamped "best before 2011" and
always work well. Maybe yours expired in 1991. The Chinese batteries at the dollar store are leaking still in their packages. I wonder how old they are. I wonder why people buy that junk.
Did you load it with anything that got hot or made the battery hot?
The cells inside a little 9V battery are skinny AAAA size and can't provide much power for very long. Anything that causes heat uses a lot of power.