Any battery damage on the board? It will likely be a light green corroded color. It can either anything from just on the holder to spewed all over the boards. Sometimes it's "not" spewed though and just has crept its way through traces so it will only be noticeable of the contacts of the battery holder and on the legs of the chips for instance.
Measure voltage coming off of the holder and also on the RAM chip with the game OFF.
I am unsure which pins you should measure across for the series of boardset/the RAM chip it uses. You can find out by Googling the name of the chip followed by "datasheet" and taking a look at the pinouts.