Hi microboard,
Some posts may seem harsh to you but to get answers you have to be able to see the whole project or the answers will be based on misleading information.
So lets look at some of the confusing things i picked up and maybe you can supply some answers to help us help you.
Lots of talk about the battery but you never actually say what your battery is. Its assumed its a SLA.
You say.
"After testing i've found with the diode theirs a fluctuation in the voltage on serial monitor but with out the diode its stable??"
What diode? Others asked and you posted a circuit (btw. Its the same as Due_unto' text version so why post it again. And where is the diode?)
Your second circuit? Is almost the same with some wires running to a text "Motors", not helpful at all.
A post with a picture of a motor would have been just as useful.
Information on the actual motor model and the motor controller model would be good as then we would have something to work with.
Finally! Some things to try.
Do you have a multimeter? What does it say the battery is doing when the Arduino resets?
Eg. Is the voltage dropping?
Can you power the motors or the Arduino from another power source?
E.g power the Arduino from a 9v battery through the regulator and run the motors off the 6v (dont forget to connect the earths on both batteries and leave the resistor divider connected to the 6v).
Set up the Arduino to output serial and send the battery monitor (A0? Your 'circuit' doesn't show) to the computer so you can see the data. Not just your leds.
So now you have done this what happened?
--To the 6v battery volts when the Arduino reset?
--What did the serial out put say whan you powered the Arduino from another power source.
(BTW you could just run it off the computer USB that you need to connect for serial)
Daz