Batteries

[Loren Beach]

Was just going to post about this. After separating the two 85AH lead acid batteries in my bank for awhile, one was at 12.3 V. The other was 9.6V. Was toying with the idea of just replacing the bad battery. I have no idea how old the good one is, but the bad one has a 2013 sticker on it.

Is it conventional wisdom to replace both batteries in the bank together?

That is what I have always heard. I recall that when our house bank of two GC batteries suddenly dropped down to about 10 volts after one night, I did replace both of them together. I figured that since I got 9 years out of them, it was risky to even think of replacing only one -- I am pretty sure that there was one bad cell in one of the two, but after all those years that "bank" did not owe me anything... !

 

[garryh]

that is the conventional wisdom. If the batteries in a bank are disparate wrt to capacity and health, they will not accept charging at the same rate and the charger gets confused and does not know what rate to charge at. One may need bulk rate and one may need absorption or float rate.

 

[debonAir]

I don't agree with the "use identical batteries" wisdom. The idea there is that when you are charging, you want both batteries to be in roughly the same shape so one doesn't overcharge while the other is still absorbing, etc. That is only true when you are hard-wiring the batteries in parallel (or keeping your battery switch on "both" which has the same effect). Parallel wiring or using "both" is just like having one larger battery right? Why buy two then? You buy two to have a backup stating battery. To keep it as a backup, you run everything off one battery and echo-charge the backup (or ACR, etc. or other way to keep it charged) and check it every so often. Lead Acid batteries have a finite lifetime and it depends a lot on how you treat them and what kind they are. Deep-discharge will generally last longer. I purposely keep my batteries out-of-sync by 1/2 a life-span so I only buy one at a time and at no time are both near their end-of-life.

All Lead batteries should have a date stamp on them so you know somewhat how long they've been in use. On the other hand a handful of discharges to something like 9.6 V will take a bunch of years off the life of a battery so the date is just another hint. The best test is to load the battery down and see how long it maintains voltage. Mainesail's (compass marine) has all the info you'd want to know about that.. but getting one new battery is an easy place to start. Id keep the other one for now.

 

[garryh]

if they are charging separately, it is a non-issue. I believe Op was talking about two batteries in a bank being charged

 

[garryh]

and if you have two true deep cycle batteries and use then alternately and never have the battery switch on 'both', one is in use and one is in reserve. No need for an expensive ACR. Deep cycle batteries can easily start the engine and then that battery is being charged by the alternator once the engine is running.

 

[Tom Metzger]

If batteries are in hard wired in parallel they do not have to be the same size, but they should be very similar in design and history. If one battery in a bank is circling the drain and the other one is good, the good one will discharge through the bad one and soon they will both be circling the drain.

Buy two batteries. If the good battery was a year or two old and held a charge you might keep it, but when you don't know it's age it's probably fairly old so scrap it.

 

[fool]

If one battery in a bank is circling the drain and the other one is good, the good one will discharge through the bad one and soon they will both be circling the drain.

Good advise for any lead based battery chemistry (LiFePO4 don’t care, add as many new ones as often as you like).

Batteries are constantly working their way back to nature’s intended neutral state. The stronger battery (or cell) will always be trying to bring the weaker battery (or cell) up while working its way down. Replace an old battery from a pair with a brand spankin’ new one and the new battery will always try to balance with the not-so-new one you left in the bank, eventually you get short changed on charge.

Similarly, a charged house bank will try to equalize with a lesser charged start bank when switched to “both” on your selector switch. A $75 to $125 dollar ACR (Automatic Charging Relay) works to prevent this conundrum without your having to think about it. The ACR will detect when the house bank has had its fill and throw some juice into the start bank. When the house bank wants more the ACR keeps the starting bank from draining back into the house. No more having to remember which position the selector switch is in while motoring down the fairway. ACRs can be had relatively inexpensively from Jeff Bezos for DIY, Blue Sea is a common and reputable brand.

Speaking of working toward a neutral state, Flooded Lead-Acid like to work themselves toward a neutral state while sitting on the shelf. These batteries will self-discharge between 10% to 15% per month. Flooded Lead-Acid also take much longer to come back to full charge than you might think, 10 hours or more is very common. Good idea to keep that maintenance charge going when away from the boat for long periods of time. AGM and Gel self-discharge at about 3% per month which puts a checkmark in their + column.

If anyone wants to weigh in on other battery types please bump the thread. Conversations on batteries can go on long after the beer is gone...

 

[Kenneth K]

Thanks for the comments. Yes I was talking about two deep-cycle lead-acid batteries hardwired together as a single ”House” bank. I have a separate “starting“ battery. I looked into installing an ACR, but can’t find a convenient place to locate it. The 1/2/All switch works fine for me and at times I like having complete control over which bank(s) is (are) charging or discharging.

Both of the ”House” batts came with the boat when I bought it, and at least one is 7 years old, so I’ll just replace them both. They are Costco/Kirkland Group 24 Marine Deep Cycle batts. Anyone know if Costco still sells these? The old ones seemed to hold up pretty well.

 

[Tom Metzger]

Anyone know if Costco still sells these? The old ones seemed to hold up pretty well.

It's as good a reason as any to buy the same brand, but the reality is that after several years the chance of it actually being the same design is pretty slim for any brand. Kirkland being a house label it may not even be the same manufacturer. Probably low bid for this year.

Costco is a good choice though because they are inexpensive and all lead flooded cell batteries are quite good. They should be, they've been making them a long time. Pay more and you may get a better battery, but on a boat sh*t happens and the better battery may not last any longer. Seven years is pretty good.

 

[Loren Beach]

Not sure about current pricing, but one reason I replaced my 9 year old Trojan T-145+ pair of GC batteries with the same model was that, at 72# each, I absolutely do NOT want to lift those heavy things in and out of the boat for another 9 years. Price is important, but it's not the only factor.

 

[Kenneth K]

.... at 72# each, I absolutely do NOT want to lift those heavy things in and out of the boat for another 9 years.

Hah. I use that as motivation to take the extra time to treat the batteries well and attempt to maximize their life.

 

[Slick470]

...I looked into installing an ACR, but can’t find a convenient place to locate it...

For a smaller and bit less expensive version of one of these battery combiners, take a look at the Yandina combiner. https://www.defender.com/product.jsp?id=605576 They are really small and come with all of the wires connected to the combiner. I found it much easier to locate in our small battery compartment than the Blue Seas version and having all of the wires there, saved a bit of effort in the install.

 

[Loren Beach]

Thanks Andy. I did read the Owners Manual (on the Defender site) for this, with its basic diagram for an OB motor. Not being an electrician I am puzzled over how this diagram might look for a small diesel inboard like ours.
We use the #1 bank on the three position switch for everything, with the emergency battery on the #2 position. The "all" position is not selected.

Then there is the shore power wiring to account for. Presently the charger is wired to each bank.
It would be great to see a similar drawing for a boat like yours or ours.
The whole "ACR" idea sounds really attractive, and someday I would like to add this.

 

[Slick470]

Loren, I think the target audience for the Yandina combiner is the power boat market because the combiner is potted and waterproof and it can be located remotely from the batteries. It works for our boat though, and was originally recommended to me by another sailor who uses one.

I don't have a picture of my installation, but I connected the combiner to the positive posts of my two banks and the negative to one of the negative posts. Any chargers connect directly to the batteries directly as well. It worked out to be a pretty simple install. They have a simplified wiring diagram on their website that ignores the off/1/2/both switch. Replace the outboard with our diesel alternator and there you go. There are two more wires, a remote switch wire and an overload wire. I didn't use either for our installation as they are optional.



I use these blue seas fuse blocks to help keep the connections to the battery posts mostly limited to the larger wires.
https://www.bluesea.com/products/5023/ST_Blade_Battery_Terminal_Mount_Fuse_Block

 

[Kenneth K]

The Yandina Owner's Manual (Owner's ManualPDF) describes one of my primary reasons for NOT installing an ACR: the need for additional fusing (see FUSES & CIRCUIT BREAKERS on pg 2). It says:

"Fuses in the battery leads to the combiner only provide protection from a short to ground on the battery cables themselves which must pierce the insulation. Conduit covering can reduce this risk. ​

​

If it is a metal vehicle and the unprotected cables are close to grounded metal the risk of a short is much higher and fuses may be a good protection. The size of the fuses has to be much higher than the charging current available because when the combiner first closes quite large currents can flow from one battery to another. These battery to battery currents are limited by the wire gauge and length of the red wires which must not be shortened. A slow blow fuse of approximately 30% to 50% of the total Cold Cranking Amp capacity of the batteries in the smaller bank is a guide to value. Although the risks are minimal without a fuse, the results of an accident can be catastrophic and even life threatening."​

​

If my two battery banks were located in the same, or adjacent, compartments, I wouldn't worry about chafing/shorting of the ACR cables that connect the two banks. In reality, they are located about 8 feet apart and the wires have to transit several separate compartments (where chafing may not be visible). The largest of these compartments is the engine compartment and engine itself (and another houses the aluminum fuel tank). Since the engine IS the ground for the boat, to me, the "metal vehicle" warning applies here.

The CCA capacity of one of my batteries is 700A. Yandina recommends a 210-350A fuse in this case. But, In no way would I expect a 350A fuse to protect the positive wires Yandina uses on their ACR--the gauge looks way too small to handle 350A (or even 200). I think the wires would fry first if shorted.

In other words, to add an ACR without adding to the risk of shorting and electrical fires may take a bit of engineering and some additional hardware. For me (with batteries banks separated by several compartments), the OFF/1/2/ALL switch seems a safer & simpler bet.

 

[frick]

I have two 100 amp type 27 deep cycle. When I put in the yanmar, the old battery box had to be moved. I put in a self in the forward end of the Port lazaret and the their wright is balanced off by the water tank of the starboard. I purchased a two battery boat charger off ebay at a great price and its even a brand name "bass boat" charger.

 

[fool]

Wouldn't hurt to ask for a little ACR help from our friend at How To Marine...

Making Sense of Automatic Charging Relays - Marine How To

Making Sense of the ACR WARNING: The ACR's in this article are not for use with LiFePO4 Batteries! What is an ACR? An ACR is nothing more than a fully automatic, voltage triggered, BOTH/PARALLEL switch that closes when charging voltage is present and opens when charge

marinehowto.com

 

[Slick470]

Fool, my understanding is that as well. That the load across the ACR is minimal. The cables for our Yandina combiner are fused, but I don't recall what ampacity. The fuse block I'm using maxes out at 30A per circuit though, so it's something less than that.

As far as the warning in the Yandina manual about metal vehicles, I think the concern is a cable chafing and grounding out to the frame of a grounded metal vehicle, which would be dangerous as a direct fault to ground which can be a high energy event. For our boats with primarily fiberglass and plywood structures chafing at a bulkhead isn't a great situation, but it wouldn't cause the same type of fault warned about in the manual.

 

[Kenneth K]

Update on Costco Batteries: Costco now sell "Interstate" brand batteries (made by Johnson Controls). My old Costco Group 24 Lead Acid Deep Cycle batteries were 85A-hr with a 3 year warranty. They lasted 7 years. The new ones are 81A-hr (though nowhere is this stated), with only a 1 year warranty and sell for $75. There is a total lack of info about the batteries both in-store and online. They are labeled only as "Marine/RV 24 DC" batteries. The clerk told me DC stands for Deep cycle. I was skeptical. I called "Interstate" to verify, and they told me that this Costco battery IS their SRM-24 Deep Cycle, 81A-h battery ($120.95 suggested retail on the Interstate website).

I did a little more research online and I really liked the Trojan SCS-150 100A-hr battery (about $229 online). Problem is, I can't find a Trojan distributor anywhere nearby, and shipping 2 batteries is over $200.

Total cost for the Trojans--about $750. Total for Costco--about $165. I rolled the dice on the Costco Interstate batts.

My local Costco also sells Interstate GP 24 AGM Marine/RV Deep Cycle batteries even though the Costco website doesn't show these. They run $170, and are only 70A-hr. I figured if I'm going to take a chance on cheap batteries, these fail the "cheap" test, so I bought the flooded ones. Time will tell......

 

[Tom Metzger]

I figured if I'm going to take a chance on cheap batteries, these fail the "cheap" test, so I bought the flooded ones. Time will tell......

Ah... I sucked in another one. Boy will he be pissed when they only last six years eleven and a half months. He'll regret then that he didn't maintain them. Of course, they only have to last one year seven months to be ahead of the Trojans.