While 6 vdc batts last longer, they can be difficult to find if one goes bad. You are now down to one 6 vdc batt and that does nothing for you. If you have a dual system of 6 vdc (4 batts series/parallel connected) you will be OK. You can delete one bank of series 6 vdc and get along. For me, 2 x 12 vdc is easier and you can find 12 vdc almost anywhere. Just my opinion.
Brenda and John
'14 Ram 3500 MCSB 6.7L HO PullRite 16K S/G, Grey Columbus 320RS Camped '14 - 146 days/'15 - 196 days
USN-EOD(Ret), Master Chief, 30 yrs,
Master Blaster of the Navy