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#494341 - 08/01/10 11:51 AM
Re: Stay with Group 24 or move to group 27 battery
[Re: Silverbullet]
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Joined: Jan 2003
Posts: 15,089
Al
Nautical Alchemist
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Nautical Alchemist
Grand Poobah

Joined: Jan 2003
Posts: 15,089
Vagabond Wanderer from Mich.
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Lead acid batteries charge in accordance to the voltage difference between the battery and charge source. Anytime a battery sees a higher voltage, it will charge to that voltage.
Lead acid battery chemistry is such that the voltage changes with the amount of charge, so the voltage supplied by the battery depends on its state of charge.
So if you connected the two batteries together in parallel without a charger or engine running, the battery having the higher charge will discharge into the lower charged battery, thereby charging it - until both batteries reach equilibrium. That means, having the same voltage, or state of charge.
This is one good reason why the battery switch should never be left in the Both position, as if one battery is completely dead, you will at best end up with two half-charged batteries.
But with the alternator running, it will also be charging both batteries, so there is some dynamic goings-on here as one battery will be charging the other battery whilst the charger is charging both batteries.
That kind of X-Y-Z thing is somewhat complicated, and at what rate one battery discharges then charges; no one knows the answer, but one battery will not become overcharged before the other battery is fully charged. The two batteries will first reach equilibrium, then be equally recharged.
Of course this only happens when the battery chemistry is the same, which is the reasoning you should not normally mix battery types.
President and CEO - Napmoor and Doolittle. 2004 Mercury 270 Dinghy. 2016 Grand Design Reflection 29RS 5th Wheel 2016 GMC Sierra 2500HD SLT 6.6L Diesel previous boats: 1995 Carver 325 1999 Four Winns 268 1999 Four Winns 225 1996 Rinker 180
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#494348 - 08/01/10 12:25 PM
Re: Stay with Group 24 or move to group 27 battery
[Re: Silverbullet]
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Joined: Jan 2003
Posts: 15,089
Al
Nautical Alchemist
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Nautical Alchemist
Grand Poobah

Joined: Jan 2003
Posts: 15,089
Vagabond Wanderer from Mich.
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A deep cycle battery is a lead acid battery. The only difference from a starting battery is the size of the plates are optimized for one task or another; the chemistry is the same, hence the charge characteristics will also be the same.
So, mixing a lead acid starting and lead acid deep cycle battery is not violating their chemistry.
And speaking of combo batteries (deep cycle and starting), some battery manufacturers, such as Interstate have gone to just a combo battery for their marine batteries. Other brands such as WalMart/Everstart still have deep cycle, starting, and combo types.
Even though Everstart and Interstate are made by Johnson Controls does not necessarily mean they are made the same. Since the Interstate is inherently a combo battery while the Walmart are separate (and less expensive) batteries, I am going to believe they are different models.
What you generally want to do is to avoid mixing battery chemistry for batteries that might be commonly charged.
That means not mixing them for the typical setup you have with engine charging both batteries via combiner.
And most marine chargers - even those that can handle multiple batteries actually charge from a common bus. One charger I am aware of can charge different battery chemistries simultaneously, and has a battery type switch for each battery bank.
But even then, charging those mixed batteries should be avoided with a combiner/engine alternator.
what should be done in that situation, say you have a twin engine boat with 2 lead acid batteries for starting and a AGM battery for the house. You should not use a combiner from either lead acid battery to charge the AGM battery, but only rely on a triple bank charger with separate charge profiles for each bank to charge the AGM house battery.
This means of course, the AGM battery can only be charged via shorepower, but hopefully it will never be needed for engine starting as you have a prime and backup battery due to the twin engines anyway.
President and CEO - Napmoor and Doolittle. 2004 Mercury 270 Dinghy. 2016 Grand Design Reflection 29RS 5th Wheel 2016 GMC Sierra 2500HD SLT 6.6L Diesel previous boats: 1995 Carver 325 1999 Four Winns 268 1999 Four Winns 225 1996 Rinker 180
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#494440 - 08/02/10 08:48 AM
Re: Stay with Group 24 or move to group 27 battery
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Joined: Mar 2007
Posts: 446
Jim_R
Vice Admiral
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Vice Admiral

Joined: Mar 2007
Posts: 446
Chicago, IL
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One question that keeps popping in my mind is how the two batteries will like each other.
What I mean is this. Both batteries will be identical. One will be the starting battery so it will see a small drain. The other will be used for the stereo so it might be discharged further.
Let's assume that my starter battery is at 97% capacity while my house battery is at 65% capacity because I played some music on the hook. Now I start the boat for a cruise and the combiner kicks in and both batteries are being charged by the alternator. Will the laws of electronics force more charging current to the battery that is more discharded or will each receive the same current resulting in an overcharge situation.
I am fairly ocmfortable that if these two were in a series, it would be possible to overcharge one battery if their capacities were different. But in a parallel situation, what would happen?
I don't think I will ever really regret buying the more expensive batteries. I MIGHT regret buying the cheaper battery. In reality, since the stereo battery and starting battery are isolated, I will likely never be stranded. Just without tunes which isn't the end of the world.
As you can see, I tend to overbuild things which often comes at a high cost of funds. Just trying to be smart about how I spend my money. As mentioned before, I have two wet cell combo batteries of different sizes, and makes. I have been running them a few seasons now, discharging them at different rates and except in off season, have relied solely on the engine/ACR to recharge them. Despite fully discharging my starting battery twice, both batteries are working great, and I have no plans to replace either in the near future. In my opinion, you'll be fine with the less expensive wet cell combo type batteries. I suppose by have two identical group 29s, like rotating auto tires you would have the option to swap house for starting batteries every season, spreading the greater wear & tear from the house system onto both.
Last edited by Jim_R; 08/02/10 08:50 AM. Reason: I edit, therefore I am.
2007 Four Winns Horizon 200 VP 4.3 GXi 225hp 2002 Bennington 2275 RL, Mercury 115 EFI 4S
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#495103 - 08/07/10 10:16 AM
Re: Stay with Group 24 or move to group 27 battery
[Re: Lou C]
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Joined: Jan 2003
Posts: 15,089
Al
Nautical Alchemist
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Nautical Alchemist
Grand Poobah

Joined: Jan 2003
Posts: 15,089
Vagabond Wanderer from Mich.
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I like battery boxes. You must use some cover of some sort over the positive terminals anyway, and the battery box does this, as well as contain any spills that may occur. The USCG regulation for battery boxes requires:
183.420 - Batteries
(a) Each installed battery must not move more than one inch in any direction when a pulling force of 90 pounds or twice the battery weight, whichever is less, is applied through the center of gravity of the battery as follows:
(1) Vertically for a duration of one minute.
(2) Horizontally and parallel to the boat’s center line for a duration of one minute fore and one minute aft.
(3) Horizontally and perpendicular to the boat’s center line for a duration of one minute to starboard and one minute to port.
Narrative: If a battery was allowed to reposition itself indiscriminately at the will of the forces that occur when a vessel (especially smaller boats with quicker motion) is operated in waves, or while being transported over land with its battery installed, the battery could become damaged. If the battery casing ruptures, the electrolyte may run out. If a battery terminal loosens, poor contact or sparking could occur. The electrolyte is usually sulfuric acid which can severely attack many metals and other materials. Such attack on fuel system components has the potential of causing fuel lines and fittings to fail and leak fuel. Movement of a battery could cause the battery terminal to come in contact with grounded items, resulting in sparking.
Therefore, the regulation calls for restraint of the battery in the horizontal and vertical directions. A battery as installed by a manufacturer may not move more than one inch when subjected to a test force for a one minute duration in each of three directions: vertical, horizontal - fore and aft, and horizontal - port and starboard. The test force selected is 90 pounds, which is approximately twice the weight of the popular size of marine battery used in small boats, which may be subject to high accelerations. For this reason, 90 pounds was selected as the maximum that needed to be applied. For batteries weighing less than 45 pounds, a force of twice the battery weight is specified. This test force is to be applied through the center of gravity of the battery. (See Figure 12).
The commercially available plastic battery boxes may be used to install a battery; however, it may be necessary to provide means within the battery box to prevent excess movement of the battery. The materials used for restraining battery movement within a battery box should be selected with regard to potential deterioration by the electrolyte. The battery box must be fastened in such a manner that the battery installation will comply with this section of the regulation.
It is recommended that the use of materials to wedge the battery in a battery box be described in the boat’s owners manual to affirm its intended use. (See Figure 13).
Figure 12 Figure 13 Some "experts" have criticized the USCG regulation as being outdated. They state for batteries like D4 size (Trojans, etc), weigh more than 90lbs, so the regulation does not apply, as it is not up to date. But I think there is a lot of good information in the regulation and narrative, and is worth following (it is the law afterall). OK, so the Trojans weigh more than 90lbs... so use some common sense and test with twice the weight of the battery... duh! If you use battery boxes (I use them in my boat), then it might be a good idea to use some 3/4" square strips of wood or Starboard at the base to help secure the battery, then use straps to hold them down (which is also the way my batteries are held down). In a sense, this is both a battery box and a tray; perhaps the best of both worlds. (Both of my Four Winns boats just had trays, no battery boxes)
President and CEO - Napmoor and Doolittle. 2004 Mercury 270 Dinghy. 2016 Grand Design Reflection 29RS 5th Wheel 2016 GMC Sierra 2500HD SLT 6.6L Diesel previous boats: 1995 Carver 325 1999 Four Winns 268 1999 Four Winns 225 1996 Rinker 180
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#495123 - 08/07/10 11:42 AM
Re: Stay with Group 24 or move to group 27 battery
[Re: Silverbullet]
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Joined: Jan 2003
Posts: 15,089
Al
Nautical Alchemist
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Nautical Alchemist
Grand Poobah

Joined: Jan 2003
Posts: 15,089
Vagabond Wanderer from Mich.
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On my battery boxes, the straps run under the tray rather than having those metal strap holders.
President and CEO - Napmoor and Doolittle. 2004 Mercury 270 Dinghy. 2016 Grand Design Reflection 29RS 5th Wheel 2016 GMC Sierra 2500HD SLT 6.6L Diesel previous boats: 1995 Carver 325 1999 Four Winns 268 1999 Four Winns 225 1996 Rinker 180
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#495132 - 08/07/10 12:24 PM
Re: Stay with Group 24 or move to group 27 battery
[Re: rwidman]
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Joined: Jan 2003
Posts: 15,089
Al
Nautical Alchemist
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Nautical Alchemist
Grand Poobah

Joined: Jan 2003
Posts: 15,089
Vagabond Wanderer from Mich.
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The box isn't screwed to the boat.
The battery boxes sit on a shelf at the rear of the aft cabin, in a separate compartment behind the headboard for the "mother-in-law" bed.
We call it the MIL bed as the boat has a full sized bed on the portside, and a single bed on the starboard side. The single bed is called the MIL bed, and is typically used for storage. We store our two bicycles on the MIL bed.
The shelf has a tray made of 3/4" wood glued to the shelf that makes a rectangle, so that the battery box fits into the tray.
The strap goes under the 3/4" wood pieces. It is pretty strong, and since the batteries are at the transom, there is not much movement anyway.
President and CEO - Napmoor and Doolittle. 2004 Mercury 270 Dinghy. 2016 Grand Design Reflection 29RS 5th Wheel 2016 GMC Sierra 2500HD SLT 6.6L Diesel previous boats: 1995 Carver 325 1999 Four Winns 268 1999 Four Winns 225 1996 Rinker 180
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#496000 - 08/15/10 01:13 AM
Re: Stay with Group 24 or move to group 27 battery
[Re: rwidman]
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Joined: Nov 2006
Posts: 4,532
trooplewis
Admiral
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Admiral

Joined: Nov 2006
Posts: 4,532
San Diego
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I have one battery in a box, and the house battery in a tray.
I like the box a lot better, and will convert the tray at some point.
The strap that holds it down with the 4 small screws, 2 at each side, secures it very nicely. It never moves, and I don't think it will unless maybe you are in a head-on collision at speed.
In which case you have bigger problems to worry about.
In terms of more expensive vs. cheap, I am of the opinion that most boat owners pay too much for just about everything, I tend to go cheap. ]
After years on this and other forums, I think it's a split verdict. Lots of complaints from folks who bought expensive gel cells or Rolls batteries that said they gave out way too early, many times el cheapo batteries lasted 5-7 years.
I don't think you can predict battery life. So I buy Wally Worlds best battery and call it even.
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CHAPARRAL
by canuckchick71. 04/16/18 12:28 PM
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