[C320-list] Looking to setup temporary 12v supply while batteries are removed?

[Scott Westwood]

I want to remove my batteries and provide a "temporary" 12v supply only to run the bilge pump over the winter.
My batteries are dying. Plans are in the works to replace both LA with AGMs before spring.
Concern: Shore power charger cooking the last dying battery and releasing caustic fumes and possible fire?  The charger dried up (boiled) the other/second battery and the fumes were real bad.
I want to remove the last battery and shut off the battery charger and run a 12v power supply if/when the bilge pump would need to run.  Right now the bilge is dry and no water leaking in but you never know.
I have one of those rolling battery charger/starter for cars and I can maybe turn it on "always on" and leave it hooked up in place of the batteries???  As long as I have shore power then the boat would have 12v (if needed).  I am not near the boat now but it is a Jabsco pump in the port cabin seat near chart table. Can't be more than 5-8 amps??
High end related second question:   Is there a permanent  battery charger that can also provide emergency crank/starting current when connected to shore power - if batteries are dead?  I know you can have a dedicated start battery but it seems silly to not have the capacity to use shore power as an emergency start power.  Asking too much?  Overkill? 
Thanks,
Scott Westwood scottwestwood at bellsouth.net H (919)-362-8538    C (919)-618-7185