Battery switch and charging question
 

What is the right way to charge batteries while running? Leave the switch to both? First run on one and then the other?
This spring I have one battery that won't hold a charge. I am going to replace both batteries. but I am wondering if I was running the switch in the proper place for keeping them fully charged.

Payton,
Either way works but works but faster if the low battery only is switched to the motor after running. The alternator charges that battery only. Both location on the switch charges both but slower. NEVER switch to OFF while running blows a diode in the alternator. Charge the low battery overnight on a slow charge then after it is fully charged test it with a load tester. If it is bad replace. Mercruiser has an electronic ignition that requires a good battery for proper operation.
Save getting stranded or fouling plugs, wasting gas and your week end replace if questionable.
Just my opinion
VeeCat

Only replace the bad battery. No need to replace a good one. That way you are only having to replace one at a time every couple of years.

Single?

I used to run on 1 battery for a day or so, then switched to the other battery. Kept both batteries from getting stale. Never did like using the Both position. 1 dead battery=2 dead batteries.

You are So right Fountain 1 !

What about a battery isolator that automatically keeps both batteries charged no matter what the switch positions?

They make models for one or two alternator setups. The alternators feed the isolator, which feeds the batteries. Then you don't have to worry about what switch is on what.

I like that idea.

Thanks for all the info guys. I was told very convincingly that if one battery is better than the other the charge will always go to the good one and the poor battery will get worse. But I don't think he was considering 2 altinaters and a battery switch.

I was going to try something similar to this. I really want to have one 12V system and not worry about keeping them separate.


http://www.amplepower.com/primer/pwrsys/index.html

There are drawbacks to doing either way. If you leave the switch on BOTH the regulator sense connection is connected to both batteries and the charging currrent is not optimal for any one battery, especially if you have two batteries with different capabilities and staes of charge. Additionally if you forget and leave the switch in both while in storage the batteries will fight each other until dead.

An isolator will work but the voltage drop accross it will mean it takes much longer running time to charge any one battery. The sense line will be connected to the selected battery but the other one will get the wrong charge profile. Not terrible but not perfect either.

Switching from one to the other is best for the batteries but you must remember to do it.

Best is to install an isolater. That way you are only using one battery at a time so that you cannot run down both without knowing. Whichever battery you are using makes no matter, both will charge at all times and only one will discharge from use.

I've never had that problem, I think it's a non issue... Don't over think this, it's a great way to go.

Precisely why many people (myself included) change batteries in pairs. When one battery begins to degrade and it's voltage begins to drop, it acts as a load on the good battery and continually drags it down. Remember, a difference of potential (voltage) is required for current flow. When this condition is present, you have a completed circuit. No different than leaving some accessory on.

WHAT??????

An Isolator is the correct solution to your problem, if you would like more descript guidance please feel free to email me.