Re: series vs. parallel
That was well put. Let me eleaborate on it.<br /><br />Draggula,the first thing I can tell you is that you have the wrong batterys in your boat. Your question tells us that. I am sort of suprised that no one picked up on it. I'll get back to that in a moment.<br /><br />Count the caps on one of your batterys. Notice that there are 6 of them, one for each cell of the battery. Each one of those cells has the ability to put out about 2 volts of power and depenedent on its internal surface area it will have the ability to hold some amount of power. No matter how big the cell is it will still only put out the 2 volts but its capacity to store energy will go up as the volume of storage material goes up - which is generally associated with a physically larger battery.<br /><br />Inside of the battery all of those little 2-volt cells are connected together in series, so the result of having 6 of those cells connected together in series is that you have a 12-volt battery. So internally it looks something like this: The first cell's positive side is connected to the battery positive battery post, but its negative side is connected to cell number 2's positive terminal and cell 2's negative side is connected to cell 3's positive and so on until the end of the line where the last cells negative side is connected to the battery's negative post. As this goes on the capacity of the each of the cells just adds up, so if the first cell had the ability to hold 20 amps of power and the second cell, to which it is connected in series internally, has the same capacity then the total capacity of the two cells together is 40 amps. So when wired in series the battery's output will be both the sum of the voltages of each cell but also the sum of the amperage capacity of each cell. So what that means is that if you connect the positive terminal from one 12-violt battery (lets say 100 amp hour battery) to the negative terminal of a second 12-volt battery (also 100 amp capactiy_ and then draw your power from the remaining positive and negative terminals (one on each battery) the result is a capacity that is going to be the total of 200 amp hours capacity and 24 volts output.<br /><br />To connect batterys in parallel is to simply hook positive leads to positive leads and negative leads to negative leads. When you do this you still get the additive effect on capacity, which is to say the the amp/hours capaictys of the two batterys will be simply added together, but you will still only have 12-volts output.<br /><br />I said I'd get back to how I knew you had the wrong batterys and so here it goes. You said in your question "The 2 for accessories are dead, and they are 780 CCA." Here is the question you might have asked yourself when you said that - what am I cranking with those batterys?<br /><br />If those are your accessory batterys they aren't cranking anything at all. It is your "Starting" battery that 'cranks' the engine, not your accessory battery(s). Now let me grossly oversimplify an aspect of battery construction so you'll understand what I'm trying to say here and also to point out a little battery choice trick that is never mentioned.<br /><br />All power that comes from a battery results from a chemical reaction that takes place where the electrolite meets the active material of a plate. Batterys that are made for putting out a large jolt of power in a short period of time tend to have lots of very thin plates. Having lots of skinny ones means that there is a lot of surface area, and that's where the power is made (I know as well as anyone that batterys do not 'make power, they store it). Unfortunately skinny plates can't hold a lot of power and they disintegrate faster than thick ones, but they do put out power. Batterys that are made to store large amounts of power, the sort of battery you would want to run a trolling motor, tend to have fewer plates, but thicker ones. They will still put out a great deal of power but they are designed to be able to do it for a longer period of time, but at a lower intensity.<br /><br />So how do you tell one battery from another? They all look about the same on the outside. Well, there is one way to tell, look at the specifications. There are a zillion differenct specifications, and they can be confusing as hell, but basically there are really only two sorts. There are cranking specifications which are used almost exclusively for batterys with lots of skinny plates and there are capacity specifications for batterys that have fewer but thicker plates. When you said your batterys had so many CCA capacity what it told me was that you were using starting batterys to perform what are basically deep cycle duty. If you are looking for a battery that will power things for hours onj end look for one that advertises its Amp/Hour rating and makes no mention what so ever of any kind of cranking power, not marine cranking amps (MCA) or cold cranking amps (CCA) or even "Reserve Capacity" which is one of the most meaningless of all of the specifications but one that can generally be converted into Amp/hour capaictiy by simply multiplying by 0.6, so a battery with an advertised Reserve Capacity of 215 amps would probably be about equal to a rating of 129 Amp Hours if it were being sold under other circumstances. Yours are 'starting' batterys, that is all I know about them.<br /><br />Thom
<br /><br />Edit: If you got to http://www.rollsbattery.com and click on [Products], then click on [Marine] you will see a little animation that is exactly what Thom is talking about. It is a 12v battery that is made up of six 2v cells
in this case they are removable 2v cells so the battery can be maintained. Some of those 12v Rolls bats with removable 2v cells cost close to $1400. They have a 10-year warranty, if that helps.
