Battery voltage drops mid cells

[Hillel Seliktar]

I have a 13s7p battery that the voltage goes up steadily but when it gets to 25v it drops to 18 and starts to steadily go up again

Right now the battery is sitting in a fire proof safe, I am not going to attempt fixing it as it's probably to dangerous but I am curious as to what happened and how to avoid it in the future.

Thanks in advance.