I don't know what you mean by a manifold battery, but my coupe has a battery box, with a drain through the fusalage, and a bolt - wing nuts - that attach the cover.
The battery is a standard A/C battery with weights in the vented caps. This is supposed to prevent spillage of the electrolyte in rough air, or in the case of a flip over... The box is made of alunimum sheet. There is a service bulletin addressing the length of the drain tube. I think this is standard fare in the Ercoupe. Later models - Forney, Alon, Mooney may have different systems. Regards, Harry
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