House Battery same as starting battery?

Hello,..


My new to me 2006 Mainship 400 Trawler has one Duracell Ultra BCI 8D Battery as the starting battery and 2 each of the same for the house batteries wired in parallel...12 v system

I thought a starting battery was designed to provide high current fast and a house battery should provide current over an extended time.


With that said, does it make sense to have two of the same type doing two different things?


The previous owner installed new back in October.

Is this a problem?

Thanks

First, if it’s a 12v boat they would be wired in parallel not series. If a 24v boat then they would be wired in series. Using 8d starting batteries is not as optimal as using deep cycle golf cart batteries but it works. I wouldn’t worry about it for now but when you go to replace I would rethink the system.

Yes, thanks error corrected...

True deep cycle batteries have thick plates, more room under and over the plates for electrolyte and caps to check for and to add water. That Duracell 8D has none of the above, so it will not to last very long.


When they do fail, consider changing them for four 6V Group GC2 golf cart batteries wired in series/parallel. Four will fit in the same space as two 8Ds. There are very few true deep cycle 8D batteries and those that are like Lifelines are very expensive.


David

Jeff, there are a lot of boats that have 8D batteries for just about everything. As David mentioned above, it isn’t ideal but it is easy for the builders initially, and it is easy for owners to simply replace like with like.

8D batteries will work for a house bank even if they aren’t true deep cycle. As David said, they just won’t last as long. Also, a true deep cycle 8D like a Lifeline will also work just fine as a start battery. It is definitely overkill, but works just fine.

Depending on how you use your boat, manage the state of charge, and how well you keep the batteries fully charged, you should get years of service out of those batteries. Don’t worry about it until it is time to replace them, then rethink your system.

Thanks for the info, I guess what got me thinking about this was.. in the past I basically ruined my house bank on my previous boat by keeping the Charger/Inverter on all the time, thats normally OK, chargers drop to a trickle once the battery voltage is stable at its set point...but in this case I neglected to keep watch on the water levels on the house bank and it eventually killed them....so on this boat, as soon as I turn off the Freedom 2K Inverter/Charger the house bank would drop to 12.2 in about 3 minuets, with minimum loading...which told me they weren't feeling too good...thats when I checked the water, they did need some so I serviced them with distilled water, and was hoping they might hold a better charger..then I noticed both engine and house were the same....thats when I started scratching my head some....

With wet cells, checking water level should be a regular maintenance activity just like checking the oil level. On my last boat I would check the level every time on got on the boat. I ran a dehumidifier in the boat full time when we were away from the boat that sat on a galley counter and drained into the sink. The drain hose ran into a water bottle that sat in the sink. When getting on the boat, I would take that water bottle and top up the batteries as a normal part of getting ready to depart.

What type of dehumidifer are you using dhays

I have a routine I do on the first of every month on our boat, and one of those things is checking the water level in the FLA batteries we have. FLA's are great, but they will not tolerate the plates being exposed from low water levels.

jefndeb said:

My new to me 2006 Mainship 400 Trawler has one Duracell Ultra BCI 8D Battery as the starting battery and 2 each of the same for the house batteries wired in parallel...12 v system

I thought a starting battery was designed to provide high current fast and a house battery should provide current over an extended time.

With that said, does it make sense to have two of the same type doing two different things?

Is this a problem?

Click to expand...

Won't hurt in the short term, replace with better (for purpose) when those go south.

Your engine manual will specify minimum cranking amps. You may find a single good high cranking amps G31 (e.g. Odyssesy PC-2150) , or maybe a pair of G31s if necessary, will be fine. And shifting the individual weight of each G31 won't hurt as much as schlepping an 8D.

djmarchand said:

True deep cycle batteries have thick plates, more room under and over the plates for electrolyte and caps to check for and to add water. That Duracell 8D has none of the above, so it will not to last very long.

When they do fail, consider changing them for four 6V Group GC2 golf cart batteries wired in series/parallel. Four will fit in the same space as two 8Ds. There are very few true deep cycle 8D batteries and those that are like Lifelines are very expensive.

Click to expand...

Thought it was six GC2s in the same space as two 8Ds?

Anyway, two 8Ds would give about 490 Ah beginning capacity. If six fit (three pairs, series/parallel to 12V) would be about 660 Ah capacity in the same space. If I've remembered correctly...

And the GC2s would really be designed for house role (deep cycling).

-Chris


-Chris

Those particular type of 8Ds are typically about 185 to 200 amp hours.
Does the boat have a parallel switch if the starting battery goes bad?

I guess I will just keep them until its time to replace,.so if they drop below 11 volts with minimal load within about 10-15 minutes they are in need to replacing at that point?

JudyP said:

What type of dehumidifer are you using dhays

Click to expand...

For years I used a 30 pint compressor type of dehumidifier. Essentially the smallest portable one you could buy. Incredibly effective. The boat was always bone dry. With all the lockers being vented, they were all dry as well.


I changed a couple years ago to using 3 small Peltier type of humidifiers. They are much quieter so we can run them while on boat and much, much smaller and lighter weight which makes them easier to move and store. I used to take the other off my sailboat and stick it in the dock box every time we used the boat. My knee doesn't do so well anymore.


I used 2 Eva-dry 2000s and 1 Eva-dry 1000. They are now 2200 and 1100. They don't have a drain hose so I drilled a hole near the bottom of the water container and used some 1/4" vinyl tubing to drain them. I had one 2000 by the galley sink and another in the head by the sink. They worked great. The 1000 I had in the forward cabin that I didn't drain. I would find that it would just about be full after 2 weeks.



One of the 2000 died after about a year and now I'm using just the remaining 2000 and 1000. They work well, not as well as the 30 pint dehumidifiers but well enough and easier to manage. If you have a place to store a 30 pint dehumidifier easily and don't mind the noise or don't need to run it when you are on the boat, they can't be beat.

The 8Ds will work ok as a house bank, just not quite as well as true deep cycles. The real problem with them is they are a bugger to replace. When they go bad replaced them with 4 6V deep cycle batteries. Oh, congrats on your new boat.

jefndeb said:

.so if they drop below 11 volts with minimal load within about 10-15 minutes they are in need to replacing at that point?

Click to expand...

Maybe even before that. Several makers say 12.15-12.2V is about 50% discharged, and if your batts go even that low within 15-20 minutes I'd say they may be past useful life.

-Chris

I know the bow and stern thrusters are fed via the house bank, I wonder if the PO installed them somewhat for that reason???

I just went through a similar exercise and posted about it. I had 2 8D batteries that acted as house and starting power to the main engine. They worked fine - no problem with starting or house power. When one died an ugly death, I vowed to remove those monsters and replace them with something more manageable. Removal was a chore. I replace the two 8D's with 4 Duracell 6v GC golf cart batteries wired in series and parallel. They fit in a smaller footprint than the two 8D's and they supply 430 ah's at 12v. There is enough room for 6 batteries but I see no need to expand my bank at this point. Overall I am very happy with the trade out, my back is happy, and my wallet is happy (total cost at Sam's Club was about $300).

Update - I asked the PO why he had the same batteries installed for both start and house and he said that these type of batteries are a "Dual purpose" type of battery.

Also he mentioned that the bow & stern thrusters use the house bank so a starting battery is best suited for that ..I would agree to that..