3rd Battery?

[Riegfrghtl]

Last week I posted a thread concerning a bad battery. I got alot of useful advice. After applying that advise I was unable to get my battery to hold charge. This weekend I purchased a Powermaster battery from Napa near the marina where I keep my boat. It is a dual purpose marine battery with 1000 mca and 160 reserve. Was able to get it at a good price. My second battery is also a dual purpose battery with a 675 mca and 120 reserve. I have a mercruiser I/O with a guest battery switch. This winter I aquired a new stereo, raymarine vhf, raymarine chartplotter/fishfinder, raymarine sattelite weather receiver. With all this new electronics will a two battery system keep up? I was thinking of purchasing another Powermaster battery like the one mentioned above. I would use one powermaster hooked to #1 for starting and use the other powermaster and other battery I have (connected in series) on number 2 as house and electronics. Most of the electrical draw will occur while boat is under power. Is this thinking okay or is this overkill. Will be doing alot of boating on the Hudson river and Long Island sound and some weekend at the Jersey shore. Any advise or opinions would greatly be appreciated. Thanks.......

Tim

 

[Silvertip]

Re: 3rd Battery?

If you have two batteries connected in SERIES, whatever 12 volt stuff you connect to that system will turn to toast. Two batteries in series produces 24 volts. Two batteries in parallel will provide 12 volts but double the capacity (provided both batteries are the same). You really wouldn't need the third battery but if you prefer to use it as well, it would be wired in PARALLEL with the other house battery. Keep in mind however that when the boat is not in use, setting the battery switch to OFF will not disconnect the the second and third batteries from each other. Therefore the weaker battery of the two will draw down the other one until both are equal. To prevent that, you could install a simple ON/OFF battery disconnect switch in the positive cable between those two batteries.

 

[NYBo]

Re: 3rd Battery?

Before Silvertip jumps in, let me tell you you would want to hook two batteries in parallel, not series, to retain 12 volts.

Whether your plan is overkill or not depends on your pattern of electricity usage, and the output of your alternator. I take it you have an I/O or a large outboard. Either will have a fairly powerful alternator that will help keep the house battery/batteries charged up. Now it becomes a balancing act: time with the motor shut down and the electronics running vs time with the motor running. As long as you keep the starting battery disconnected using a battery switch when the motor isn't running, you will be okay if you run don the house battery. Just turn the switch to the starting battery, start the motor, and off you go. If you end up running down the house battery before you'd like, add a second. I would use a matched set, although that's not an absolute must.

EDIT: Crud! Silvertip beat me to it. Gotta learn to type faster!:facepalm:

 

[Riegfrghtl]

Re: 3rd Battery?

Thanks Silvertip, I meant to say parallel but the hands could not translate what the brain was thinking. You gave me some food for thought. I will see if third battery will fit and then go from there. May just get the new battery and keep the older one as a spare. Thanks again!

Tim

 

[Fireman431]

Re: 3rd Battery?

Just to verify, you want your batteries wired like this:

 

[bassman284]

Re: 3rd Battery?

Before Silvertip jumps in, let me tell you you would want to hook two batteries in parallel, not series, to retain 12 volts.

EDIT: Crud! Silvertip beat me to it. Gotta learn to type faster!:facepalm:

Well, he's quick.

 

[NYBo]

Re: 3rd Battery?

Well, he's quick.

Yeah, he's fast and I'm just half-fast!:redface:

 

[Silvertip]

Re: 3rd Battery?

Everybody else "types". I "copy & paste". How do I do that? I have canned answers for all of man's questions. Some of them actually make sense!