adding a 2nd battery

[johnzonh]

hi guys.... I have a spare battery from a previous boat...hate to see it go to waste so I want to add it in to the system..and give it the ability to recharge, start if necessary, or power the radio on occasion. I have room on the other side of the engine to put it... wondering what I need to get to do it. I have a marathon Falcon '87 mercruiser 165 3.7 (yes, the black sheep of mercruisers) I have seen a few wiring diagrams but would like to hear some input. No battery switches in the system yet.

 

[Grandad]

It's a good idea to have a second battery. I use 2 batteries with a single selector switch that I can use to choose between at intervals to ensure that each remains freshly charged and confirm that each is able to start the engine and perform fully. You can get elaborate charging systems that will require sharing the charger, but all you really need likely in your case is a simple selector switch wired appropriately to add the second battery. - Grandad

 

[Bondo]

Ayuh,.... Just get yerself a battery switch, some heavy cablin', 'n hook it up as the house battery,....

There's plenty of 1, 2, Both, battery switches out there,..... Mine's a Perko I think,....

The grounds are all run to the motor block, the positives run through the switch ya gotta buy,...

 

[johnzonh]

oh ok. sounds good. yeah it has just been collecting dust but it has been accepting a charge. Might as well use it

 

[Power_house]

Here's the battery switch I used to add a second battery, I also ran 2ga wiring for positive and negative.