Join Date: Aug 2006
Location: Arlington, VA
Thanked 14 Times in 12 Posts
Rep Power: 12
They're supposed to be. 8D's do vary considerably by weight, depending on construction details, but they should be pretty close to a standard size.
Isn't there anyone you could trust to measure the ones you have?
Another option might be to use other battery sizes while you're at it, like 6V golf-cart batteries. With a little ingenuity, it's sometimes possible to squeeze in more amp-hours in just about the same space, and to do it using batteries which won't break your back like 8Ds will (e.g., 70lbs each instead of 150lbs each :-)