In your pictures, the Z80 ram is that thin chip BR6116 below the SM1 ROM, the board says 6116 in white text next to it.
wiki.neogeodev.org
See here in this article, the Z80 error means a connection or chip issue is present between the Z80, the SM1 ROM, the 2K 6116 SRAM and the YM2610.
Some of the needed traces for these chips are near the battery, it is very common for battery leakage to destroy those traces, a person would have to patch over these traces with wires. In severe battery damage cases, the YM2610 and the traces underneath it can get destroyed by corrosion.