You're best off cleaning them mechanically (brush or rag with wd40 as suggested) rather than chemically. If you try and etch the surface you'll either create lead waste solution which really shouldn't go down the drain, or fail to remove the oxide since neither lead chloride (muriatic acid) or lead sulfate (battery acid) are very soluble. A rag with vinegar actually works okay since acetic acid dissolves the oxide, but be sure to not wash it down the drain.
If you do any dry brushing of the lead be sure to do it in a well ventilated area and always wash your hands and work area well after handling it. Lead poisoning is a legitimate concern especially when handling corroded lead.