This shows a battery that is very low in voltage, about 11.5 vdc… barely enough to start the engine.
Alternator brings about 25 amps of current into the system (orange line) and the battery’s voltage starts to recover (blue line).
Here I turn off the engine, and the battery’s voltage falls right away. That is not supposed to happen. So, then I turned on the boat’s charger. This battery is no longer able to store any energy. ((Even though all its cells are flooded and test fine with a hydrometer.))
Underway, normal operations like using the bow thruster, were causing all the electronics to reboot or turn off due to the extreme voltage drop. (A 25A alternator is not enough to power a bow thruster. Its job is to charge a batter that CAN power the thruster.)
It got fixed today!
I used a 4x mechanical advantage block and tackle to get the 140 pound 8D starboard battery out of the engine room. Dockmate, Bobby helped me get it off the boat and into the car for return. A “bank” of medium sized G31 batteries will replace this one large one. They are much easier to work with and give increased capacity combined than the single large 8D.
140 pound 8D battery lifted out of engine room with block and tackle.