Help. Battery question

[jrslost@aol.com]

Battery question. 25’ cabin cruiser. 200 hp OB. dual bank. 2 house. 2 Start. All 4 sea hawk start battery 1050 MCA. I have seen this before as recomended by battery manufacture and mechanics as new start batteries are now built as dual purpose batteries to elimate the three types, start, deep cycle and dual purpose. they stager thick and thin plates in battery as a dual purpose is but called a start battery. ?????? Prove me wrong

[ssobol]

Both batteries in my 22 are dual purpose FLA. Work fine for everything, but I rarely have them less than 85% SOC. One battery is used primarily, the other is reserve. If I have have been anchored out for awhile with high electrical usage, I'll parallel the batteries for an engine start, just to be sure I don't drag the bus voltage down too low when the engine cranks (this upsets some of the electronics).

[thataway]

I am not sure what the question is. Yes, I also like to keep batteries the same, at least for two batteries (or 4)from a single charging source. In the C Dory, I will use two group 31's, and an ACR/VSR to combine the start and house battery. I may also have a separate set of specific batteries for the inverter, or high draw items like refrigeration or freezer. These will not be identical to the start battery, and usually charged with a battery to battery charger.

[T.R. Bauer]

I can't prove it either way, but what describe sounds like a compromise battery. And that is probably just fine as it gives you a situation where have some of the attributes of true deep cycle and also starting. I don't think this a new idea.

In regards to eliminating a FLA battery type? I don't think that is going to happen in the near future, but I may be missing what you are saying. In my opinion they all have a unique purpose and are good at what they do. For example, I wouldn't want any thin plates in a battery that is never going to have start anything - the trade off being able to start something comes at the cost of being able to deep cycle.

As Bob noted, a DC to DC charger might be smart if you have different types and sizes of batteries in the mix since it is possible to overstress alternators and wiring. In your case, it may or may not matter that much, but even 4 identical batteries in need of some amps could be an issue for your system. I generally figure a group 27 battery that is 50% discharged will accept about 10-20 amps, so take that 4 times in your situation and if they are ran in parallel, this may exceed the limits of your charging system.

[Donald Tyson]

New to this:
Do you need to disconnect each battery and charge separateley or can they be charged as a bank?
What is an inverter? Basically a transformer?
Usually once I start asking immature questions it follows that someone recommends a book to study and I'm hoping you won't disappoint this time. I'll be wanting dependable supplies of juice and haven't the faintest Idea of how to go about that.
I use a trolling motor every week, with a storage battery, until it is dead. Then I switch to the second battery until its dead. Then I go home and clean fish. I understand firsthand that it would ruin a starting (thin plate) battery.
I have a million more questions...

[Tom Hruby]

If you have the choice I would recommend having a separate lead acid deep cycle battery for the house loads and a starting battery for the motor. Charging can be from the alternator with a switch from one to the other. The other option is to charge the house battery from shore power and the starting battery from the alternator. There are several reasons for this.

1. If you discharge a starting battery below about 60-70% of its rated capacity it will have a very short life span (# of charge discharge cycles). I don't know the exact number but it probably is less than 100 cycles or 1-2 years. Also, if you fully discharge a starting battery more than a few times it is toast.

2. A deep cycle battery can be discharged to about 40 - 50% of its capacity for about 500 cycles. If you fully discharge it, it may last less than 100 charge cycles and last no more than a year or two. The data I have seen is that discharging a deep cycle lead acid battery to 20% of its capacity (20% SOC) its lifetime is only about 200 - 250 cycles.

3. In my opinion, a hybrid (dual purpose) has the problems of both types without providing any benefits.

[thataway]

Generally it is not good practice to use a battery until it is dead. I monitor all of my battery systems--usually using Victron negative shunt type of meters--primary blue tooth to the i phone is a easy way. I try and not let flooded lead acid (FLA) batteries to discharge more than 50% or a voltage of 12.2 resting steady state--no power taken out or put in for several hours. There are batteries which can be discharged far deeper with little harm

I have been using LiFePO4 (lithium iron phospate) batteries for about 10 years. On our last 25 we had a bank of two 100 amp hour batteries which would give about 180 amps of usable power thru an inverter to run the microwave and induction burner for cooking. We also ran two chest type of freezer/refrigerators which ran on 12 v DC(prefered on the boat) and on 120 V AC when at the dock, or when charging the batteries. We had a DC to DC battery charger to provide the charging current off the outboard motor of about 30 amps per hour.

I have a setup with one 100 amp Li battery DC output, DC 10 amp charger and a 30 amp charger off the vehicle battery--with a 35 liter chest freezer/ref. that we keep in the car. It can keep frozen meals for a number of weeks of my diet. Or it can take a number of lbs of frozen food from the supermarket to our home.
I used a cheaper battery for this, than the boat.


I am currently building a 400 amp hour system which will power our home freezer, charge computers and mobile phones etc, plus give minimal light in our home--and can run our well pump in an emergency. This is in case there is a prolonged power outage and for some reason we loose fuel for our "whole house, 18 KW generator" (which powers all of the systems in our house when we loose mains power--like in a hurricane.). I got my current set of 100 amp hour batteries for a little under $200 a battery. I paid over $1000 for the first 100 amp hour battery over 10 years ago. I won't go into the various brands, and safeguards in each brand etc. But I used Will Prowse's video's as a baseline for what components I bought. The system will have a 3000 watt pure sine wave inverter, 400 watts of solar power, and a 50 amp mains power battery charger, or 30 amps off a vehicle alternator (RV or SUV). I have a 1000 watt Honda generator and that can run a mains power battery charger.

There is a young man named Will Prowse who has a U Tube channel dealing mostly with exotic batteries, solar, inverters and chargers. That is where I would start--give you a long time learning.

Will Prowse solar power forum/web site.

And from his video channel on basics of electricity

Starting here you can learn the fundamentals, and go forward.j

An inverter is a device which converts DC battery power (can be other sources) to AC Main's power (similar to what you get from the power company). The DC power is turned into AC power, using a "H" bridge and transistors, and then the AC power uses a transformer or solid state device to boost the voltage to 120 or 240 volts. Grid power in the US is 60 cycles a second and most of the World is 50 cycles per second= 50 Hertz (or cycles per second).

There are several ways that inverters work, and variable purity of the sine wave type of power. Cheaper inverters used what is called stepped sine wave. The best inverters give power which is a smooth sine wave, without "interference".



That information should get you started. After all of that, I can recommend a book... in the next installment.

[Tom Hruby]

I agree that Lithium Iron Phosphate batteries are the way to go for house power, and I have been using them as my main power source, and house power, for 12 years now. However there is one major issue with them:
NEVER HOOK ONE UP DIRECTLY TO YOUR ALTERNATOR. Always use a separate DC - DC charger. The Li battery can take a much higher initial current and that can stall out, and kill, the alternator. Also, the charging profile is different and a Li battery should not be "floated."

[Donald Tyson]

Would there be a less advanced way of saying all this Tom? Kinda think I know what youre saying but not sure and it seems like it is very applicable.

[Tom Hruby]

OK Don,
Let's get into the weeds. Battery technology and chemistry is constantly changing so one needs to do a lot of research before using Lithium batteries for starting. If you are not willing to specifically match a certain battery with the outboard motor and its charging circuit, I would suggest sticking with a lead-acid one.
First, if you are considering a lithium chemistry for a boat, I contend that Lithium Iron Phosphate (LiFePO4) is the only chemistry suitable for a boat. I won't go into all the data supporting this conclusion but you can find it on line.

The questions that you need to ask if you want to use a lithium starting battery are as follows:
1. Does your motor have a stator or alternator for charging? The former have the potential for more issues that really get into the "weeds." From what I have seen on line, it seems that most motors under 100 hp have stators rather than alternators.
2. What is the maximum discharge rate in amps of the battery relative to the current needed by the starter? Most inexpensive LiFePO4 batteries cannot put out enough amps to start the motor.
3. What is the maximum rate for its BMS (battery management system)? Sometimes the less expensive batteries may have a BMS that cannot sustain the starting current.
4. Your charging system may have maximum voltage that is less than that needed to fully charge the Li battery.

Up until 2022 Mercury Marine stated that Li starting batteries were not approved. More recently they have approved them for some of their motors. But, the battery specifications are quite stringent including a waterproof rating of IP67 (can withstand submersion for up to an hour). Most LiFePO4 batteries are only rated to IP 65. There are few "starting" batteries that have an IP 67 rating.

I found an interesting you tube video that explains some of these issues.
https://www.youtube.com/watch?v=SudTi5xZSgo

[-Waypoint-]

I have twin BF40s on my boat. One engine produces 17 amps of usable charging power. I use the ECOFLOW River Pro power station. I bought a 300watt pure sign wave inverter to charge it up to 200 watts of AC output. That's the max amount one engine can charge with keeping the voltage at 14 volts. This unit runs both of my Engels fridge/ freezers for 16 hours. So with a lager outboard one could charge a power station much faster. I wanted to keep my electrical system portable in case I needed for the house and other applications.

[Avidmagnum12]

Definitely more than one way to do this. I run 3 type 27 duel purpose AGMs on the C-Otter. While they can be split to a start battery and 2 house I generally run them as one big 270 amp hour group. I have a Engel freezer and the stock fridge that came on the boat. Running fans, lights and chargers for electronics mean that I’ll get to 60 to 70 percent SOC overnight. I monitor this carefully. It’s a simple setup and it works for me. The last set of AGMs lasted 6 years.

Almost every CD-25 I’ve looked at have different battery setups. Everyone has different power needs. I do not use an inverter. If I need 120 we start the Honda 2000…..and that’s not often. We do have 250 watts of solar which will keep everything going on a “0” day if it’s sunny.

Lots of good ideas presented….

[Schuster]

jrslost, getting back to your original question/challenge. There are several articles which will help to determine what the various battery make ups consist of and although some can be used interchangeably they could cause damage to the system if the wrong combinations are used. What I am getting from this is that STARTING batteries have thinner plates that in the short term put out high amps but are not designed to release continual but lower amperages. I'm uncertain of what the consequences are if you are trying to use a starting battery for a long term house application, but I suspect that it may not end well. Same goes for trying to use a deep cycle battery as a starting battery, as they are not designed for that purpose. The dual purpose batteries are just that, designed to accomplish both tasks. But, are they as effective as their counterparts that are specifically designed to accomplish each task separately?
In my 25 I have 3 batteries, 1 starting and 2 house. The house batteries are dual purpose. I don't mind that as sometimes I forget to switch from house to starting and I don't feel that I am doing the house batteries harm by throwing a high demand on them as opposed to deep cycle batteries. so far it has worked out well for me but I suspect that the dual purpose batteries won't last as long over the long haul. We shall see.











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