Boy is that last sentence important---especially if you are using any lithium chemistry. While cycle life of lead acid is compromised with dead battery episodes, lithium batteries are often dead permanently when that happens---if you're lucky, they may come back, but reduced capacity & higher internal resistance need to be watched out for.
I just dodged a bullet (I hope) in this regard. Here's the story:
I installed a single 3kw nom. 42v lithium Enerdel module in my boat, motored it around for an hour or so, then hooked up my 36v golf cart charger and walked away figuring the charger would shut off at between 40 and 42v as it did with lead acid. Next day decided to go check it out to be sure---the pack voltage was up to 48v and the charger was still on (maybe 1amp). Fortunately, 48v is still under the fully charged voltage of the pack. After a jaunt around the island, I disconnected the AC side of the charger & left the pack at 45v. About 3 weeks later, I went out to the boat to find that 45v had decayed to 3.5v. My heart sank…I disconnected that module & plugged in my other one, then went out on the river with that just to at least enjoy the day. I discovered that the golf cart charger's DC plug had been still connected to my pack and that this was evidently enough to discharge my pack in 3 weeks---that never happened with my nom. 70-100ah lead acid pack, which is just weird. So I disconnected the charger altogether and took the depleted pack home. Over the past week I gradually recharged the depleted pack, which was registering 13.5v when I got back home. I started with nom. 175ma into each 48v half of the pack until it reached 20v, which took about 1 hour. From 20 to 28v, I increased the charge current to 300ma---at this point the pack had reabsorbed about ½ AH of charge. At that point, I began charging at 4.2a & enabled the BMS to the pack as the voltage increased slowly from 28v to 45v. I saw no problems, minimal self-discharge & each half of this pack has absorbed about 33ah of charge at 45v. They are rated at 35ah at 48v, so I'm feeling pretty good about the capacity not being lost. Will have to see how they act over time, but at this point I'm pretty impressed with these cells and not inclined to throw away the investment.
Anyway, always always verify how much load is remaining on your pack, if any.
-Myles
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of forums@greensdomain.com
Sent: Saturday, November 16, 2013 9:57 AM
To: electricboats@yahoogroups.com
Subject: [Electric Boats] RE: practicality ?
Most answers have talked about charging with solar/wind/etc., but if I understand your question, I would say don't worry about it. All the battery types discussed here slowly self discharge over time, but a few weeks or even a few months is not a problem. I use four 105Ah AGMs. The first year, I charged them every few weeks over the winter, but the charger entered its final stage immediately. I now charge them every few months over the winter, but I think I could go the entire winter without charging at all and still have 80% left. Just make sure no power is being used while you are absent.
Pat
---In electricboats@yahoogroups.com, <jlwuja@...> wrote:
Good Day,
I'm in the thought process of an electric repower of my boat. Most everything says I should convert based on numbers. One of the considerations, absenteeism, just hasn't been addressed in the sources that I've utilized.
So here's the question, if an boat owner can't visit a boat for periods of time that could run up to two months on occasion coupled with more frequent absences lasting several weeks, is there a better battery choice to be made?
In another two years or so, I should hope to be able to pay much more (almost daily) and long periods of absenteeism would virtually be eliminated.
Should I wait to do the repower? I have a perfectly working diesel presently.
Thanks for your informed responses. John
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