looks like you put them in series, that should make your voltage go down, run them in parallel and it should make it go up =)

The higher you are above 12v the better you are because chargers run more efficient at higher voltages, which basically means less heat in the charger. As long as you are above 12v though for most chargers you will be good to go =)

As far as amp draw check out the ammeter in your dmm, those are usually rated to 10A, and mine measures about 18 to 20 before the fuse blows =P (shh I didn't tell you that)