I purchased a new 36V ebike in 2020. The 36V 8AH battery has diminished to less than half its range giving me 7 miles instead of 20. Since the company was out of stock on new L ion batteries at $249 a piece. I purchased 3 12V 9AH lead acid sealed new batteries exactly same brand wired them in series to make a 36V 9 AH battery using new 10G stranded wiring and connectors and hooked it to my bike. Fully charged it gives me 10 - 20 minutes ride time or about 1/2 mile. Can you tell me what’s wrong?