I did check the switch with key OFF, and turned on just headlights, (New working bulbs !).. The v did drop some 2 or 2 /5 v,.... I forget exactly/ Probably NOT good!!
Did it drop at the battery terminal?
If so, try a long slow charge. 2 amps or less if your charger has a selector, or if its automatic, you can let it do its thing overnight.
If it didn't drop at the battery, then its good enough for the testing you're doing.