the er models run a different charging coil. Every time my battery got low in my er sled the tack went nuts. I think you need to change the charging/mag coil out. maxdlx
I read somewhere that the ERs didn't have built in filters in the wiring because the battery eliminated the need for them. The regular vipers had these filters installed to smoothen out the chg cycle. See a dealer cause it causes other issues.
One the vmax deluxes the same problem occurs dead battery screwy tach. The sx I have has a big capacitor up under the cowling and I don't that the deluxe has it. Just double checked my memory and it was right. Look at roonies the electric start does not have the smoothing condensor. J