Some diodes have a lower forward drop, or possibly some mosfet diode replacement may have a lower forward drop.. But certainly the current handling ability must be adequate.

 

Okay, so I have given this conundrum some considerable thought, and have come up with the following solution.



What this does is isolate the battery from the PA's power board when the unit is plugged into the mains, which is when the battery gets "over-charged" by the crappy charging circuit. Mains power is also applied to the new "Intelligent 3-stage Battery Charger" by the relay, which also connects the battery to the charger's output terminals.
So I believe that solves all the problems...

1. The battery only ever gets a charge from a decent charger, one that can be left connected indefinitely.
2. The battery is available to the PA speaker when it is not plugged in, and that's the only time you will ever need battery power.

Does this seem reasonable ?

 

YES, that seems like a totally reasonable scheme for saving the next battery. Just verify that the relay selected is rated for continuous operation.

 

YES, that seems like a totally reasonable scheme for saving the next battery. Just verify that the relay selected is rated for continuous operation.

Good point, it will be permanently energised when on mains power, I need to check...

 

Good point, it will be permanently energised when on mains power, I need to check...

Nothing on the datasheets for the relay I've ordered says anything about continuous operation... so I'm guessing it's OK

 

It should not be too difficult to add a temporary mains connection and power the relay for a few hours and see how warm it becomes. Then you will know.