[trit21]

Aetna tachs are ugly IMO, digital red led's on a 2000 is just not pretty, will always look like a replacement. True analog are not always perfect but they are repeatable and look better IMO. BUT, as far as the tach's bouncing around, sounds like you have a ground issue. I had the same problem and one of the ground wires on the sensor boards was causing intermittent buzzers and the tachs to jump around.

As far as the batteries, verify voltage at the battery with battery charger both off and on. Verify voltage when running engines at battery charger. Voltage gauges at the helm again are not entirely accurate but you are looking for a change when running and absolute numbers are not needed. There are 2 relays behind the helm that activate when you start the engines and they are for the voltage meters, if they have corrosion on them then they will show inaccurate, low or unstable. If you take some voltage readings I can guide you through as I had to troubleshoot various little issue like this on my 2000 3500 Open and finally got everything worked out.

Tom