T-Pain Is On A Boat: Re: [Electric Boats] Battery Life and Types

Sunday, September 12, 2010

Re: [Electric Boats] Battery Life and Types

This is an interesting discussion chain. It reminds me a bit of my thoughts when I look at light bulbs and the advertised hours of life. My conclusion is that no one will ever tracks light bulb hours and I suspect the same will be true of many of us in our applications.

In my case my launch probably only gets to run 20 or so times a year. I have Lifeline AGM's that are advertised at 1000 cycles. If I get 1000 charge cycles someone else will have to track the last 500 cycles.

I would also note that there is a new AGM being manufactured in Australia that they claim better than 3000 cycles along with a better power to weight ratio.

In my case I do typically draw down to 40% or thereabouts.

On the yachts there are the casual weekend users that Chris notes that probably have similar or less usage than I do and then the year round cruisers like my sister. In her case the charge cycles will pass more quickly however the drawdown is highly variable. It will be a very rare case that replicates whatever test the manufacture's use to predict life cycles.

That gets back to the question of how long each of theses technologies will last independent of theoretical number of charge cycles. As noted I do not expect to be around if my batteries last 50 years but I would almost be willing to bet that they will have to be replaced long before I "fall of the perch".

I would also expect that the life not only will vary between technologies but as with the typical lead acid or AGM will vary greatly between manufacturers and the quality of their materials and production.

On Sep 11, 2010, at 4:53 PM, Chris Baker wrote:

Hi Owen,

There are other aspects of Lithium batteries that offer advantages over lead acid batteries.

One characteristic in particular that is useful, particularly for solar powered boats is their tolerance of remaining in a partial state of charge. When discharged to low levels even as low as 10% state of charge they do not deteriorate while in this low state. And depending on your circumstances an electric boat can spend a while with the batteries only partially charged.

Consider a simple weekend's boating... you leave the dock wit the batteries fully charged say on Friday evening and head for your favourite anchorage. Getting there reduces the charge to say 70% and you then stay at anchor for two days before returning to the dock. So the batteries spent two days only partially charged.

We see lots of information about how you should limit the discharge of your batteries for extended life, but not much about how long the batteries can stay at a particular state of charge, and how that length of time may effect longevity. But t does seem that this kind of treatment is detrimental to lead acid batteries, but not in the least to lithiums.

In the case of a solar powered boat the effect is even greater because the batteries may take many days to be recharged, especially in inclement weather.

I don't know of how you might quantify this effect, but it is real, and would have some effect on life expectancy.

Cheers

Chris

On 09/09/2010, at 10:45 PM, otyers wrote:

I intend to convert my 27' 7000lb sailboat to electric over the winter.

I've been reading on this group that lithium batteries should have a
~2,000+ cycle lifespan compared to ~750 for AGM, but I've also read that
one should only expect batteries to last 5-7 years. Does this 5-7 year
life expectancy also apply to lithiums? If so, it would appear that one
would need to more or less discharge the lithium pack every day for it
to make sense (365 days x 5-7 years = 1825-2555 cycles), otherwise the
capacity for these extra cycles would not get used.

For those of us that are lucky if we get out on the water 30-50 days in
a year (a range of 150 - 350 discharge cycles over a 5-7 year period),
what battery type would make the most sense? Also, any tips on where
to source these batteries inexpensively?

Thanks for any advice.

Regards,

Owen