Thinking of switching to Li Ion batt. Looking for feedback/advice

NCKA is a huge resource with all the varied people we've got so I thought I'd put this out there:

I'm just in the thinking about it stage, it's expensive but the size/weight/longevity seems really attractive compared to the SLA I currently use.

I'm not an electrical guy but as near as I can come with:

My FF draws .615A at 12V and I've found a Li Polymer Battery that is rated at 77wh and can be set right at 12V output.

If I understand the calcs 77Wh/12V = 6.4Ah which ought to run my FF for about 10 hr. (6.4Ah/.615A =10.4hr)

So my questions

Are there "holes" in my thinking/calcs?

And is this battery a good choice/are there better choices.
http://www.batteryspace.com/li-ion18650boxbattery12v-132v77wh4aratewithregulatorandlowbatteryalerttrailtechplugsmartcharger.aspx

Other advice or thoughts?

http://en.wikipedia.org/wiki/Lithium_battery

http://batteryuniversity.com/learn/article/safety_concerns_with_li_ion

The evidence is mixed, but I can't say I would want a Li-Ion battery in my boat.  I recently saw a Li-ion batteries at the San Mateo Motorcycle show and they looked very light for the voltage they put out.  So for my Hawg I would use one, for my kayak not so sure.

I use LiPo. 5ah would last me all day, but I'm never on the water for more than 8 hrs at a time. Batteries rarely provide the capacity they're rated at. 80% is about average.

The thing to know about Lithium batteries is that if you short them, they generate a lot of heat, usually would melt and catch fire.(Protected cells are slightly safer, but I don't think there's any Lithium battery that is 100% safe.) You don't want it burn a hole in your kayak while in the water. With that said, I think with proper water protection, I still prefer Lithium over other conventional batteries. It is light weight, high current output, minimal drain during storage (I hate SLA or alkaline for the crazy drain in storage), and the list goes on.

The one in your link seems overkill and expensive, and I doubt it can withstand water spray very well. I use a RC type 14v Lipo 5ah battery and it's only around $35 (and a generic balance charger for $30). I put it in my Hobie plastic bucket and it stays dry. I also use a 20ah Lipo for my 18lb trolling motor somethings. Battery and motor together weights only 13lb. Lasts me 6+hrs when trolling at 2mph. I love Lithium batteries. Let me know if you want pictures of my setup.

ernest

Lesson learned is don't tear appart a sealed battery pack near water.  Guess its sealed for a reason, huh?!?!?!

Do note that a number of marine, handheld electronic devices currently USE li-on battery packs ... food for thought.

I have more questions and comments,

First the batt will be in a 100% waterproof container. (or at least as close to 100% as I can get for those of you who want to argue [like me])
 
This one has excessive discharge protection that ought to minimize some of the risks.

The one I chose says Li Ion, there's an almost identical one (74wh) that says Li Polymer. Can anyone explain the difference in laymans terms?

I've read up on the safety stuff and figure I'll be OK/ or I'm OK with the risk.

I use lipo's for my RC heli's and they are a pain.  They are great because of the light weight but you need a special charger just for them, they are not suppose to go below a certain voltage when used or when they are just sitting around and if they get pierced look out.  When pierced they shoot out a flame that is very hard to put out, you have to remove all the air in order to put them out.  When you are not using them they need to be stored in a fire proof box that is tightly sealed for protection.

They have great benefits, but you must be extra careful with them.  I have seen first hand what can and does happen when you are not careful with them.  A buddies garage burnt down while charging, he left them to charge on his own and they ignited.  and he has been using them for years.  You are suppose to stay with them as they are charged at all times or charge them in a sealed fire proof box.

I am not trying to scare you off but telling you the truth from what I have dealt with.


Here is some basic differences:
http://www.lipohobby.com/article-111.html

Here is more info:
http://www.instructables.com/answers/What-is-the-difference-between-Li-poly-batteries-a/

And if you really want to geek out, which I highly recommend:
http://www.allaboutsymbian.com/features/item/15775_How_do_Lithium_batteries_work.php

So stick with Li-ion....

after all this....i am going home and kissing my *brick SLA batt right on the terminals and tell it I love it!
 

+1... SLA's good enough for me!!! If I'm that worried about the weight I'll diet off the difference

Thanks to all and especially Scott for the input.

after all this....i am going home and kissing my *brick SLA batt right on the terminals and tell it I love it!

I'll probably just put a little "blast door" on my battery box and call it good.

+1... SLA's good enough for me!!! If I'm that worried about the weight I'll diet off the difference

Probably a better plan,,,,,,,,,,,,,but still,

7 pound SLA vs 1.5 pound Li-ion.   

I use a helicopter battery. 4000 . I can fish 5 to 6 hours easy. and ready to get off. the best thing I like is I can charge it with my charger off my 12v car battery.
But on that note in High School in chemistry class the teacher showed what lithium will do in water. A fellow student took about 1/2 lb. He threw it in toilet and flushed the toilet. Well needless to say some plumbing was replaced. So i very careful when charging. I keep it in a water proof box. Maybe I should put it in two boxes. 

Couldn't open the attachment.

How about lithium iron phosphate, like this one:
http://www.batteriesinaflash.com/lithium-iron-phosphate/12v/k2-energy-k2b12v7eb-12v-7ah-lithium-iron-phosphate-battery-bms

These are supposed to be stable (none of the heat/meltdown problems of lithium ion) and fairly lightweight (about half that of SLA). Of course they are very expensive---it's $99 for the plain vanilla version, while the one at the link above includes some overload protection circuitry (highly recommended from what I read) and it's $139. Supposedly, they'll last a lot longer than SLAs. Anyways, it's probably not worth the high price. However, I suspect they'll come down in price in the not-too-distant future, so it might be something to watch for.

Thanks, for anyone else interested the one above looks good too, it's also dimensionally the size of most of the little SLA bricks were used to, just without the weight, I think this listing says about 1/5 the weight. But still $139.