I have 8d batteries hooked up for 24 volts, how many can I hook together before I have to break it up to smaller groups each battery is 255 amp hours

So you have a 2040 ah 24 volt battery bank. Wow! and Kewl,

I am running 1170 ah bank with 810 watts in panels and have little problems getting to float charge each day. So long as you can make them float you are ok. However, for safety sakes you should put a disconnect on each string of 4 batteries. I have no math formula to back this up nor have I found this in the NEC (which I have a copy), I just get spooked. I have a 12 volt system and have 9, 12 volt batteries with a disconnect on each three. This allows me to take three or six batteries off line for cleaning or what ever. Mainly it just makes me feel better because they are there no matter how useless they are if there is a short out. The correct way is to put a fuse or breaker on each battery.