My boat has 2 unconnected electrical systems. How can I charge the starter battery from the domestic one?

Get a battery switch as suggested, one for 2 batteries. Connect the ground wire from the engine and the rest of the 12 volt system to the ground on one of the batteries. Connect the positive from battery one and connect it to the pole on the battery switch thats labeled one. Connect the positive from battery two and connect to pole on battery switch labeled two.Connect the engine positive and the rest of the 12 volt system positives to the pole labeled feeder on the switch. Connect the automatic 12 volt positive wire from your bilge pump or pumps directly to one of the batteries. This way the pumps will always have voltage avilable even if you have the batteries turned off, which you should when you leave the boat. Now you can run the boat on either battery or both at the same time and charge them by whatever you select on the battery switch. #1, #2, or "both".

Yuo can use a battery switch as mentioned above.

A m uch more elegetn solution is use a proper battery amangement system. Sure these cost a few hundred ££ but they monitor all the batteries and ensure you'll never get stranded with all your batteries dead. and boat builder will know about these are they are fitted to the majority of new decent boats.

Mu old boat used to have the 1,2 or both as above. My new one has the full works and i'd never go back. I've got 2 starters, 5 domestic and never have to think about the batteris , the unit does it all for me.

First you will need a battery charger. You will notice the battery charger has three chords. One plugs into the house current. This is a three prong chord with two flat and one roundish terminal.

The others are one red and one black wire. The red goes to the battery post marked with a plus sign. The black goes to the post marked with a minus sign. (+) (-).

Plug the battery charger into the house outlet.

Pop the top inspection plugs out of your battery. (These are also for adding water.) If level is low add distilled water to the top of the slot going down the inside of the hole.

Now place the black clip on the post marked -. Then place th red one on the post marked +. Now turn the charger on to the low setting. Let the battery charge.

Be sure to read the instructions that come with the charger.

And do not get the liquid from the battery on your skin or clothes. It will burn you and eat your clothes. Also please note, the gases that are emitted while the charger is charging are EXPLOSIVE! So do not smoke or bring an open flame around that battery while it is charging.

you can purchase a marine battery switch @ any marine store. This Will allow you to have two batteries. you didn't mention weather you are using a trolling motor with 24 volt. If so you will need to do more research and a lot more wiring. Most outboard motors have limited charging and trolling motors will exceed their output

I'll probably be proved wrong but I don't think it is possible to do that!

You'll have to connect a charger to the starter battery.

There are plenty of options depending on your setup. Email me if you want to know more. I am a fully qualified marine engineer.

sounds like you have a generator. if so, buy an "isolator" and connect the two. if your local boat store isn't familiar with them the rv place will be.