Batteries?

Xplicitlnck

Xplicitlnck

Well-Known Member
Jan 2, 2012
4,030
Long island ny
Boat Info
330ec
Engines
Twin 7.4 straight drive
I wanted to add one or mayb even 2 more batteries to my 270 da. I was wondering if it would be safe to have a single engine (one alternate no generator) to charge 3 our even four barriers Idrop anchor and listen to the radio for hours and hours on end and would also like to run the fridge and a blender so looking for more battery life? Was going to just mount one battery next to the other and jump pos to p pos and neg to neg? Would this b the right way to go it? Thanks everyone
 
Yes, pos to pos and neg to neg is correct to maintain the same voltage but increase the amp hours available. There will be no problem with having one alternator charging threee batteries. It will only charge at the top of it's ability. It will just take quite a bit longer to get all three to full charge.

What you might want to also consider is a good battery charger that will let you bring all the batteries to full charge before you leave home.
 
Also by doing this you may want to consider a battery isolator... that way if you have one battery take a dump it won't ruin the other two... they are not terrible expensive either... just a thought
 
Your idea is a good one if done right. Yes your alt will charge all three, but it will take a lot longer. My suggestions are;

1- Keep one battery (or bank) soley for the engine. This way if you drain your other one (or two) you always have a battery or a battery bank isolated for your engine.
2- A "smart" battary charger is highly recomended to continously maintain and charge your bats when not in the water. At least charge before and after each outing.
3- Use deep cycle bats to run the "house". The engine starting battery can be a Cranking bat.
4- Setup the ability to parrallel (join) your "House" bats and your "Starting" battery using a parallel switch. This will tie all your bats together as an emergency backup for your "starting" battery.
 
Well thanks again for everybodys help don't know what I would do or how much I would spend if I didn't have this web site and everybodys help thanks again
 
also... best idea is to keep the batterys the same amp rating, ideally bought at the same time, same brand, same type. the reason is if you stick a 300 amp battery in parallel with 2 -250 amp batteries your 300 just became a 250. the batteries will level themselves out charge wise. again a battery isolator should stop this problem. as mentioned above, your alternator will charge them all but it will be slower than just one battery.


sams club is selling a 15a three bank marine battery charger for about $110. remember that while in parallel, with no isolators, any battrry charger would treat them as one battery.

also as mentioned, isolate a starting battery so you are hopefully never stranded!

for security i have a set of jumper cables on board, hopefully ill never need to use them!
 
Thanks again for all your help got the three batteries isolated and installed another job done summers almost here
 
You probably have a 55 AMP alternator. That is what I had. I replaced them with 70 AMP because the wires out of the alternator were not good for any more AMPS. If your alternator ever goes you might want to concider upgrading it. Make sure the mounting points are the same and the pully will line up. The way I see it if you have 100 AMP hour batteries and have 3 of them from dead batteries you will need to run your boat for 6 hours with a 55 AMP alternator to charge them. Others with more electrical knowledge can probable give you a more accurate charge time based on your alternator and battery type. I have two group 27 deep cycle batteries per engine and after running them for 4 hours they become fully charged.
 
Xplicitlnck said:
Thanks again for all your help got the three batteries isolated and installed another job done summers almost here
Click to expand...

Good deal. I think nothern makes a good point as well... keep in the back of your mind.
 
Definetly will keep it in mind does mercruiser make a70 amp our do I have to go with adif company? If so do you know of any body that makes them? And when you say the wires only hold 55amp do you mean the internal alternator wires our the external?
 
They were after market alternators. On my last boat, 28 footer I had the altenators rebuilt to put out a bit more power, but buying new worked out better. The more AMPS you put through a wire the bigger the wire needs to be. The person selling you the alternator can probably tell you what wire size you need for the alternator you are buying. To big an altenator the wires can burn I have been told.
If your alternator fails take it to the Mec dealer or marine supply store and see what they have. An auto alternator is not designed for marine use I have been told never put auto store electric parts on the boat as they could blow it up because of open sparks inside.
 
Another thing you may want to consider is a battery monitor. It is a big help so you do not have to guess how many amps you have left in the batteries. You also learn what on your boat causes the most drains on your power supply. I used the Victron BMV-602s demonstrated below because it was so easy to wire in place. Works great.

http://www.pbase.com/mainecruising/battery_monitor
 
ardeprint said:
Your idea is a good one if done right. Yes your alt will charge all three, but it will take a lot longer. My suggestions are;

1- Keep one battery (or bank) soley for the engine. This way if you drain your other one (or two) you always have a battery or a battery bank isolated for your engine.
2- A "smart" battary charger is highly recomended to continously maintain and charge your bats when not in the water. At least charge before and after each outing.
3- Use deep cycle bats to run the "house". The engine starting battery can be a Cranking bat.
4- Setup the ability to parrallel (join) your "House" bats and your "Starting" battery using a parallel switch. This will tie all your bats together as an emergency backup for your "starting" battery.
Click to expand...

+1 I had over a 1000 watt system on my 22 footer and did exactly what you posted. Worked well. there were times when I would drain the house battery but I always had another to start the motor and get home. Once home I would put a battery charger on the deep cycle battery and was good to go the next day.
 
Sounds good just one question I have the factory battery selector switch off one both two if I start the boat with just one once the boat is running is it safe to switch over to both? Or do I have to shut down to move the selector?
 
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