3.0ltr Batteries?

[Welsh Rob]

Hi Again,<br /> <br />Could anybody please let me know what size batteries i should be using?<br /><br />It is a yr 2000 model 135hp mercruiser alpha drive.<br /><br />Electrics on board are gps,sounder,vhf,and nav lights etc<br /><br />Boat is set up with twin batteries and as i have only just bought her i want to replace both with brand new to give me the peace of mind....<br /><br />Therefore what is the correct sizes req,ie starting amperage cold cranking,and amp hour ratings?<br /><br />Not sure of the wiring configuration,boat is in as new condition with two isolator switches but no changeover system,so would prefer to use two batteries of the same size!<br /><br />Many thanks from Wales Uk.<br />Rob.

 

[Peter J Fraser]

Re: 3.0ltr Batteries?

Rob,<br />My policy with batteries is:<br />Always fit the largest unit(s you can get into the space available.<br />Check carefully with your supplier as quite often you can get same size cases with more plates installed. This is a good option as you have more cranking power (CCA) in the same size case.<br /><br />Peter

 

[Welsh Rob]

Re: 3.0ltr Batteries?

Hi Guys,<br />The reason i was asking for specfics is that i read somewhere that if the batteries you fit are too large with too much cca then you can put undue stress on your alternator!<br /><br />Can anybody confirm this please?<br />Thanks

 

[oxbowman]

Re: 3.0ltr Batteries?

Don't believe it. When the boat is running, you are running off the alternator not the batteries.

 

[craze1cars]

Re: 3.0ltr Batteries?

No such thing as a battery that's too big unless it doesn't fit in the hole. The system will only take as much power as it needs when cranking, the rest just stays in the battery and provides you with more reserve. High CCAs won't effect the alternator or starter at all...just make sure they're 12 volts. I believe the Mercruiser spec for a 3.0 is really low, something like 375 CCAs I think??? Someone please correct me if I'm wrong. ANY normal sized marine battery will provide much more than that since most provide 525 or more. You say you already have a twin battery setup, and it sounds like you have minimal accessories that don't put a lot of draw on them (no trolling motor?), so I personally don't think a pair of monster batteries is extremely critical for you.<br /><br />Fish around in the "Electronics" section of this forum and you'll find all kinds of recommendations and experiences with different types and brands of batteries to help you make a choice.

 

[Peter J Fraser]

Re: 3.0ltr Batteries?

Rob,<br />You should really look at also installing an automatic charging system that will keep both batteries fully charged when your engine is operating.<br />The real simple units use heavy duty diodes to equalise the charge but there is a very slight voltage drop across the diodes so your alternator will not be able to fully charge the batteries.<br />The best systems use 3 master switches (3rd switch for emergency parallel) and a voltage sensing device to monitor the battery voltages and charge them accordingly. This means that you dont need a big capacity alternator as only one battery is being charged at a time.<br />Your start battery always receives the juice first and then switches to your house battery automaticly.<br />Have a look at the link on my signature line and you will find a photo of the electrical setup Ihave installed on my project.<br />Good luck.<br /><br />Peter