Battery Charging

in the old days it was reasonable recommended practice that the battery caps be removed when on a mains charger.

there are two reasons.

the old style mains chargers generally had higher open circuit voltages and poor regulation..so at the end of charge the voltage could be quite high and the battery would gas far more vigorously than it would on the vehicle generator or alternator.

the second reason was that state of charge was generally assessed by observation......"Charge till the battery gasses freely"

to observe this you had to look down the hole, to look down the hole the cap had to be off.

cheers

Oh there is a third reason.
Because screw top batteries require topping up.

If the caps are off, and the owner looks inside to check for free gassing.
they would also be likly to observe the fluid level.

Screw top batteries can loose quite a bit of fluid under charge.

The best time to top up a battery is after it is charged.

cheers

If your have nothing running off the aux whilst it's garaged then occasional trip will probably be enough and no top up required.

I would be more worried about the cranking battery, and leave it on the charger, if you do this then it it is a simple matter to make up a jumper so that you can charge both batteries at the same time.

Leigh

Just an example:
If a small solar panel or even a big one was attached periodically or full time it will charge the battery as will a battery charger doing the same.

RE 240v chargers
Many use a 240v smart charger if it is going to be left on and not supervised as they do cut off and trickle when full charge detection is achieved.

Solar chargers (if reg is a smart one and chosen correctly) will do the same float when battery is charged.

If using the charger on a dual batt system, some method of ensuring both are being charged is required if both have to be charged at the same time.

If it is the main being charged AND you have a VSR Voltage sensitive relay, it should connect the aux when the main has reached the "connect" voltage and drop out when it goes below when off charge.
There are other many methods and combinations possible.

Others will add to these comments with their preference of system.

If a battery will not hold a charge for 14 days with nothing connected..its well buggered.

lots of people seem to have the need to have their batteries constantly on charge.

as long as there is no load conneced, preferably the battery isolated there is no need for constantly charging, in fact it could be argued that it reduces the life of the battery.

cheers