Please don't hurt yourself.
Many people do not realize it but there is a LOT of energy in the batteries and they can be very dangerous if abbused.
Abuse can be asking them to product more current than they were designed to.
Lower resistance puts a huge strain on the batteries. They sometimes fail by giving off gas, hot enough to burn. Carefully check the resistance of your coils, and have someone with experience who knows what he is doing check things out.