High Charging Rate. Found Voltage Drop Need Guidance Please

I don't see an issue with running the tests. 5- 10 minutes run time. If you see voltage following rpm, keep the rpms down.
If you want to run some drop tests with engine off, you can check the run circuit, and the battery feed. You won't be able to check the alternator feed.
When you're done put the battery on a slow charger.

I don't know how you executed your wire around. If nothing was disconnected, then ammeter discharge is probably correct, but battery charge will show nothing.
For voltage drop checks, follow both paths. Makes tracking a little more complicated. But in both cases should end up at the ignition run wire. So maybe start there.

Ten years is a long time on a battery. Your doing good. A load test or an acidity test will show how much capacity it has left.