Steel Soldiers now has a few new forums, read more about it at: New Munitions Forums!
Microsoft MSN, Live, Hotmail, Outlook email users may not be receiving emails. We are working to resolve this issue. Please add support@steelsoldiers.com to your trusted contacts.
In addition to what was said about batteries, they can check good voltage wise but not support a large current discharge. Use a carbon-pile tester to check.
Start with the basics, how are they wired? Neg(-) of the first Batt to ground(frame/chassis), Pos(+) to the Neg(-) of the next Batt. Finally the Pos(+) of the second Batt to the starter?