Originally Posted by PaulRivers

If you were taking the battery on and off the bike all the time I would suggest a single 4 cell battery and using the y splitter cable as you suggested for sure. Way easier to just take one battery on and off the bike.

And if you want to do that to save money, it's certain a decent option. However, I used to do that myself - a Dinotte 600 in the front and the 140 in the rear with the splitter cable. Then when I found myself very dissatisfied with the 600L and Dinotte was nice enough (wonderfully) to let me send it back and switch it for 2 400l's, where (because of power requirements) I had to run a 4 cell in the front and a 2 cell in the back.

I found that not having to mess with the y cable running down the top tube to be way easier. It didn't droop down. It didn't get caught on anything when moving the bike around. It didn't get pitched when I put my bike on my bike rack and cinched it down. Etc.