Are you wanting to 'replace' one 12V battery with two 6v batteries?
YES...wire the 6V batteries in series
Are you wanting to 'add' two 6v batteries with your existing 12V battery?
YES....wire the two 6V in series and in parallel with the 12V battery
Is it time for your medication or mine?
2007 DODGE 3500 QC SRW 5.9L CTD In-Bed 'quiet gen'
2007 HitchHiker II 32.5 UKTG 2000W Xantex Inverter
US NAVY------USS Decatur DDG31