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Old 28-12-2009, 08:23   #1
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Battery Cycles - Time for a New Look?

Marine batteries traditionally were looked at in terms of cycles. A 100AH battery cycled between 50-80% would last for so many cycles. This was because charging was done with the engine or generator, and that was kept to a minimum due to cost, noise, vibration ect. But the question in my mind is
"is this really the way to look at it today?"

Most cruising boats will have a number of ways to charge the batteries, or to run straight off the charging source. Solar, wind, water can supply most if not all of the power a typical boat would use. For instance, I have currently 2 100 watt solar panels, but plan on adding 2 130 watt panels for a total of 460 watts, plus a wind generator. This combination should make our boat run off alternative energy completely, or mostly so when the wind and sun cooperate. When they don't the alternator on a engine, or a generator, either gas or diesel will kick in to fill the gap.

So what really happens at the battery level when talking about cycles, when this occurs? I ask because, it will mean a big difference when talking about when to change the batteries.

If most of the load is handled by the solar/wind setup, how much does the battery "CYCLE"? If one were to start with a fully charged battery, and made sure to fully charge it say once per week or month, wouldn't the battery just act as a shock absorber for the electrical system most of the time?

What would that do to the battery's life span, either FLA or AGM? And which type would be better to handle that load in terms of life expectancy and performance in cost vs AH vs total life expectancy?

What other factors are there to be considered ?

This is more than just a exercise to me. The savings in battery's and replacements can be considerable. For instance, I used to have a 800 ah bank, but now expect the same performance with 500 AH or less. at what point would the system be under powered?
I don't have the real life experience, and will not be able to long term cruise for more than 3 weeks or so for 10 more years, so mostly I will be hooked in to the dock most of the year, where a small bank would be fine. But for those times when on vacation for 3 weeks, and when I can cut the cord and cruise full time, this is my question.

People that are out cruising at using a similar setup, I would be interested in hearing what you have to say about this.
Thanks,
Bob
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Old 28-12-2009, 08:52   #2
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In my own experience, I have found that standard deep cycle lead-acid batteries that have not been abused last for roughly 5 years. So if you are not doing relatively deep discharges it may be better to think of their lifespan in terms of time.

I consider a battery to be worn out when it will no longer store anywhere near as much energy as it did originally. I realize that's kind of a vague definition but it has worked for me.
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Old 28-12-2009, 09:17   #3
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Bob,

I know you're thinking ahead, but in 10 years the energy situation will likely be VERY different than it is today, based on all the advances in both storage technologies and generation technologies. Several wonderful things are happening right now with batteries, with more expected soon. Likewise, solar panels are likely to become much more efficient in the near future. Nano-coating, inter alia, will help make some great leaps forward.

Bottom line: for what you say you're doing for the next 10 years, i.e., limited to 3-week cruises, I'd just lay back and enjoy things, without worrying about the future. David M is right: figure about five years for flooded batteries in cruising service, treated right. Some last a bit longer, some less. For flooded batteries in essentially storage mode (dockside, always near full), you could get more...maybe 8 years or so. Other things intervene: stratification, sulfation, corrosion, contamination, etc. So, you can't call it much closer than that.

The best batteries for standby service (like UPSs) still seem to be gels. They can easily last over 10 years. I have two golf-cart gels in my basement now which spent over 10 years on a boat which only did weekend cruises, I used them for battery tests over a two year period, so they're now almost 13 years old and test VERY well. Two others, from the same batch and with the same treatment, test less well....about 60% of capacity.

Bill
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Old 28-12-2009, 10:44   #4
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Correct me if I'm wrong, but I think it was always based on charge cycles because for every amp in and out some of the lead plate disappears in the process. eventually the plate is too thin and porous to work anymore..essentially a battery is a "corrosion machine".....it's job is to corrode creating electricity in the process... My experience says 5+ years Gel maybe up to 7 wet cell.... Unless they sit unused too much...
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Old 28-12-2009, 11:46   #5
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Quote:
I used to have a 800 ah bank, but now expect the same performance with 500 AH or less. at what point would the system be under powered?
Under powered would be when you can't through normal use keep the battery bank above 50% before doing a full recharge. A 50% discharge will yield the the highest integral value of all cycles over full battery life. When you have too many batteries you never get them fully charged and when you have too few you discharge them too deep. You can operate at higher discharge rates and lower then 100% recharge rates but it's not in the best interest of your wallet.

The idea is have only the number of batteries you really need and no more or less for the sweet spot. Batteries you don't need still die some time.
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Old 29-12-2009, 07:47   #6
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Paul, true. But what if the bank rarely goes below 80% due to the solar and wind supplying most of the energy required on board?

Bill, I agree. The future looks very promising in both solar and battery technology. But since I can not foresee what ultimately will be available at a price point we can afford... I posed the question.

I guess I am just asking how long the darn things will last when not cycled in the traditional sense. Because most of us these days do not do that kind of cycling anymore.

Bob
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Old 29-12-2009, 09:40   #7
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Quote:
But what if the bank rarely goes below 80% due to the solar and wind supplying most of the energy required on board?
It could indicate your bank is too big. Batteries age if you use them or don't use them. More deeper cycles will age them quicker but there is still the issue of age alone no matter what use they get. I know of well cared for Trojans that go more than 7 years. The dealer I use says he has had them last 10 years since you can tell the date of manufacture if you know where to look. My experience has been 7 years.

If you can manage your power needs with say 4 golf carts (lots of people do) adding two more won't extend the life of the bank proportional to the added cost even if it did extend the life of the bank. Reducing consumption is still more effective than expected technology changes. The key is to need less power.

This is where a battery monitor helps since it puts real numbers to your usage and allows you to really know the state of the bank and manage them better even though the monitor does nothing on it's own to actively extend the life.
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