If your charger is small enough to be carried aboard your boat you can leave these cables in place since the charging procedure requires it.
Charging 24v system with 12v charger.
As far as charging boat batteries on the water test your system on land and always use the correct size fuse and proper gauge wires safety.
While most vehicles use a 12 volt 12v electrical system many buses and some boats utilize a 24 volt system.
In the examples below two 6v batteries in series 12v.
The batteries look like this.
There are many options available to purchase but i would stick with a marine option that is designed to be in wet environments.
I have a 12 volt battery tender here.
Alternatively you must arrange that contacts b and c make first energising the relays before the charger is connected.
The 24v systems that employ 12v batteries can be recharged with a 12v alternator by simply being plugged in like any other 12v battery.
While selecting the correct charger to charge and maintain batteries which are wired in series using genius or gen chargers the battery system must equal out to 12v unless using the 24v mode on our larger chargers the batteries must equal 24v.
I ve already tried connecting them and in the second picture is the only way that the battery charger will actually charger it will not charge any other way that i connect them.
If your boat has a 24 volt battery system it probably has two 12 volt batteries that are wired together so that the negative post of the first battery connects to the positive post of the second battery.
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With this system you must make certain that the 24v or 36v which will for an instant be applied to the 12v charger will not damage it.
You can use a 24 volt charger or a 12 volt two bank charger.