How I grumble about using derivatives for analysis (frown) . Connect 8 D cell flashlight batteries and Tah-Dah you have 12 volts. For dainty hands, Harbor Freight has a true adjustable carbon pile load tester. The 2nd best way to accurately test a lead acid battery. Parts store cheese grater load testers are as useful as a treadmill with a recliner chair.
I've seen batteries that will exhibit 12 volts
Put a 20 amp load on them and they slump to 0.00
Load test batteries at 50% of their cold cranking amperage rating.
Welcome to the world of a ruined vacation :(
