2 good starting batteries in series work fine; 3 good starting batteries in series is enough to blow holes in 3/16" plate.
Use heavy duty jumper cables (should carry these any how) and a decent rod holder/stinger on a separate piece of welding cable (jumper cable clamps do not want to hold the rod well).
The jumper cable clamps can melt their way into the battery terminals.
A cautionary note; lead acid batteries can emit hydrogen gas under high discharge or charge rates (danger of battery explosion; although so far it hasn't happened to me).
I favor a #10 welding lens in a pair of cutting goggles.
Get a chipping hammer. A cheap inverter powered angle grinder would not be out of place.
A section of 1 1/2" or 2" PVC pipe works fine to store the rod (rubber caps are easier to remove).
Most of my battery welding is done with 1/8" 6010 or 6011 rod; but 5/32" 6022 deck rod (recommended for flat horizontal use only but works for me everywhere) works about the best for me (normally available, locally, only in 50 pound boxes).
When the rod catches fire reverse the polarity.
When the rod sticks, check the connections and/or recharge the batteries.
I thought about setting up a spare alternator under the hood for welding and winching (and 110 volt, NOT 60 cycle) power) but since it is rare that I do/need any of the above, it hasn't been worth the trouble, for me.