I came across this while I was browsing the web, others here might be interested: marazuladventures.files.wordpress.com/2013/01/diy-lithium-iron-phosphate-batteries8.pdf
Very interesting article Bruski.
Li batteries have a fantastic power to weight ratio, making all kinds of things like mobile phones, notepads and drones possible.
Not long ago I worked on a project involving 100kW of lithium batteries in a submarine. The possibilities of what might happen if the batteries ever got immersed in seawater, punctured or the charging went wrong, had me in a cold sweat (and the other engineers) every time I went near them.
In the article, and referring to the battery box, if that boat rolled and their battery box filled with sea water and had AGMS there may be some serious fizzing and hissing and maybe fire potential. If it happened with Li batteries you'd be totally relying on the current limit electronics in the batteries (if they have it) protecting you from kaboom. Too scary for me. 
See this
I just finished reading this PDF on AGM and it states in the PDF that AGMs do not like topical heat or any thing over 25 C as I was considering using them
www.batterydirect.co.nz/uploads/images/pdfs/Batteries-Demystified.pdf
Hmmm thats a strange thing that he wrote. Maybe there are some dud versions of AGMS out there.
The ones on Trek have a design lifetime of 12 years and 3 year warranty. The present pair have been in for two years now and are OK. From their data sheet it says this
Can be mounted at any angle
Spillproof
Maintenance-free
Low self-discharge (less than 3% per month) at 25degC
Voltage: 12V
Nominal Capacity: 80AH at 10 hours
Max discharge current: 800A (5s)
Design Life: 12 years
Dimensions: L260 x W173 x H218mm
Weight: 24kgs
Warranty: Full 3 year manufacturers warranty
Incidentally I design charging systems etc for that co. I'll have to ask whats up with that comment??!!
When I was buying house bank AGM batteries recently, the shop staff asked where they would be located. They said their stock was not suitable for locating in the engine area due to high heat - doing so would void the warranty. We got in others that were warranted for higher heat locations (engine compartment, under bonnet in 4WD etc). However, the issue identified was not effect of ambient temperature, it was fire resistance of the battery casing...
Just when you think you've got all factors considered...
I have just completed a swap out of AGM to Lithium house bank, The AGMS were not keeping charge as well as they used to .
www.ev-power.com.au
Thank you everyone for the feedback, given me lots to consider, however still got lots of time to make choices, so lots of time for thought. 
Select to expand quoteHG02 said..
I just finished reading this PDF on AGM and it states in the PDF that AGMs do not like topical heat or any thing over 25 C as I was considering using them
www.batterydirect.co.nz/uploads/images/pdfs/Batteries-Demystified.pdf
Quote form that PDF above below
The limitation of the AGM battery is an inability to cope with high ambient temperatures as experienced in the tropics. Often you will find in the small print of warrant terms and conditions – ‘Warrant period is halved if this battery is used in temperatures exceeding 25ºC for more that 10 consecutive days’ – or similar
There are videos on Youtube of lithium batteries starting diesels. Easy enough to have a lithium battery close to your Bukh and used for nothing but starting. I have a lithium starting battery in my race car that weighs 1.5 kilo. The earth strap weighs the same!. I'm amazed at the cranking power of this battery.
HG,
My anchor winch runs off the 400amp/hr house bank , but I have a optima yellow top separate starter battery for my 2 outboards with its own charger.
Ill be giving the Lithium's a good work out starting next week , and will let you know if any issues arise especially when using the anchor winch etc.
Select to expand quoteDAMA said..
HG,
My anchor winch runs off the 400amp/hr house bank , but I have a optima yellow top separate starter battery for my 2 outboards with its own charger.
Ill be giving the Lithium's a good work out starting next week , and will let you know if any issues arise especially when using the anchor winch etc.
Thanks Dama
HG,
Spent just over 2 weeks cruising up the coast , No issues with the lithium's working the anchor winch daily (1500watt motor) or the 12 volt Microwave either , voltage never went below 13.1 volts . After the 15 days away plugged in the charger and only needed to top up 15-20% , I do have solar but quite a few days were overcast .
Thanks Dama
I have a two bare battery compartments except for one wet cell
I wonder how a wind gen can be wired in
Note that Lithium Iron (LiFe) are a completely different animal to Lithium Polymer (LiPo) batteries.
LiFe batteries can pretty much be used as a direct bolt in replacement for lead acid batteries, whereas LiPo batteries are a lot more fussy. LiFe have a lot lower chance of catastrophic fire. Most videos you see of "Lithium" batteries catching fire are LiPo.
New battery tech is amazing 
They are indeed great high performance batteries, while they are happy, and the electronics in them is working. And Nebbian is right, the newer chemistries are getting safer. But this is the problem....
www.watoday.com.au/national/western-australia/perth-mum-warns-parents-after-baby-monitor-explosion-20160818-gqvhry.html
www.theguardian.com/business/2015/aug/19/lithium-battery-review-boeing-dreamliner-fire-heathrow
www.dailymail.co.uk/travel/travel_news/article-3203423/Fire-Boeing-Dreamliner-Heathrow-caused-airport-close-runways-caused-trapped-battery-wires-led-short-circuit.html
And remember the batteries above were supposedly tested, good quality and safe!
io9.gizmodo.com/heres-why-lithium-batteries-occasionally-just-catch-fir-1711514559
A bit like gas on board. Its great as long as its under control. Because I design electronics to control Lithium batteries often, and I know electronics fails quite easily and what happens when it does, for myself I prefer to sleep on the boat not thinking about fuel and electricity fire sources under my bed. And I especially dont want to be at sea with a calculated risk on board when I can have very low risk and use AGM and metho.
Strange response, Trek. As Nebbian pointed out, LiFePO4 are a quite different technology from LiPoly and LiIon. LiFePO4 "are a huge improvement over lead acid in weight, capacity and shelf life. The LiFePO4 batteries are the safest type of Lithium batteries as they will not overheat, and even if punctured they will not catch on fire. The cathode material in LiFePO4 batteries is not hazardous, and so poses no negative health hazards or environmental hazards. Due to the oxygen being bonded tightly to the molecule, there is no danger of the battery erupting into flames like there is with Lithium-Ion." -see here: www.batterystuff.com/kb/articles/battery-articles/lithium-battery-overview.html
None of the examples you linked to involved LiFePO4.
And could you elaborate on the dangers from lithium batteries and seawater alluded to in your earlier post? I'd suggest that there would be virtually no risk at all of any ill-effects in a low-voltage system. I don't know much about submarines, but I'll bet their propulsion systems are several hundred volts, this of course would be different with risk of chlorine generation. [edit - no, my mistake: chlorine is only a possibility from mixing seawater with sulphuric acid. Not a problem with any type of sealed battery]
The main dangers of LiFeP04 batteries relate to the high energy density and low internal resistance. These risks can be managed, and these qualities are also what attracts us to LiFePO4 batteries in the first place.
Fair comment, but like I said newer chemistries are getting safer.
I also referred to the risk, NOT guarantee of a fire hazard. When out alone on the ocean I think minimizing risk is prudent.
Further, none of the examples I linked to were about LiFePO4 because a given sailor might put any kind of Lithium battery on his boat. I was not limiting the discussion to only one type.
Unless there's a new Lithium Battery that I don't know about ALL lithium batteries rely on built in electronics working properly to share current between cells, prevent them overheating in a short circuit condition or charging error condition and possibly heading into a fire situation.
If the electronics fails, and it does, the user probably wouldn't know. There is NO self test on any lithium ion battery I have ever seen. If that happens and the battery and/or associated charger/circuitry is immersed in with conductive saltwater or put under excess load another way, the possibilities could be catastrophic.
Re LiFEPO4 batteries not catching fire ..... I dont think so.
Read this article which quotes:
We have a smashed safety glass window in our workshop to prove that LiFePO4 Lithium batteries can explode and catch fire if overcharged. Or more importantly over-discharged and then recharged without checking for a dead cell. We know of at least one other vendor that has had a similar experience. Also there are many examples of battery fires where no BMS was used or where an improperly designed BMS was inactive or failed
www.ev-power.com.au
And take a look at this LiFEPO4 battery fire:
www.batteryvehiclesociety.org.uk/bvsorguk/forums/viewtopic.php?t=1825
My own belief is that LiFePO4 will eventually replace lead-acid as the system of choice for marine house batteries, but they certainly aren't a drop-in replacement. At the moment, anyone using them needs to be well aware of the technical issues, have an understanding of Ohm's law and its implications, and be prepared to be hands-on with monitoring and management. These batteries are far more prone to damage or destruction from overcharging or overdischarging than lead-acid are.
In a marine house-battery situation, with much lower charge and discharge rates than are typically seen in EV applications, the consensus seems to be that a full BMS with active balancing is unnecessary and probably undesirable. Monitor individual cells, have an alarm if any cell voltages vary by more than a few mV, and have emergency disconnect relays for overall over or under-voltage seems to be the arrangement that most use. There are some ongoing threads over at Cruisers Forum, mainly this one:
www.cruisersforum.com/forums/f166/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069.html
(But make a strong cup of coffee first, it started in 2011 and there are now 355 pages!!)
BTW my main interest is in DIY systems built up from individual cells. I'm aware that you can now buy pre-packaged 12V systems with a BMS incorporated, which are marketed as being direct lead-acid drop-in replacements. I have some reservations about these as the charging regimes required, although pretty similar in some respects, aren't the same.
Forgot to elaborate on the dangers from lithium batteries and seawater alluded to. Seawater is around 25 ohms per cm as you would know.
I made my comment at the beginning of this thread about the risk of battery box pictured filling with water. At 24V, with wiring on side by side terminals, a 1cm gap between +24V and 0V is not uncommon. A 1cm gap between terminals on a circuit breaker is not uncommon. In each place seawater could allow 1A to flow that shouldnt.
Everywhere theres a 1cm gap 1A unaccounted for power can flow. If the spacing is less (not uncommon) more current can flow. If the length of parallel conductors is greater more current can flow. The batteries in the pictures have substantial lengths of bare conductors.
If that battery box filled with seawater substantial currents would flow everywhere amongst that battery set potentially charging / discharging the batteries into who knows what state. The batteries would wind up in a very uncontrolled state of charge. Apply charging current to the mess and what other people have reported could happen. If the BMS (battery management system) is faulty there is especially a real risk then.
OK, will have to take your word for it - the units of resistivity and conductivity have always confused me a bit. I have read somewhere a discussion that suggested at 12V, leakage currents through seawater should be negligible but cannot find it now.
The surface area of the exposed conductors will also have a big effect of course.
I would hope that after full battery immersion, anyone with a LiFePO4 batt would check things before applying a full charge (goes back to my previous comment about understanding being important given the existing state of the art).
I agree with you that LiFEPO4 or something newer will replace Lead Acid because they are so much better. And if coastal or inshore racing with a light weight boat where the weight saving made a difference I probably would even use them. Offshore mmmm not sure.
My nagging on is because I have seen boaties of the sail and motor type do scary things with electrics and putting high power batteries in their hands could have undesirable results because they are blissfully unaware of how to treat them
I think keeping to 12v there will not be much of a problem. At the moment lead acid batteries are cheap and mounted low are convenient although you have to concern yourself with the angle they might spend time at. The lithium batteries make sense when they are used mounted close to the units they are powering. They weigh very little and can be mounted at any angle. I can see a big future in the marine sphere. At the moment they are in the powerheads of electric outboards and I can not see why they would not be suitable to power electric anchor winches. They can be of a portable nature and charged at home or elsewhere on the boat. Clipped into position they would have enough charge to raise the anchor several times. I also think a lithium power pack might be worth carrying to power radios and nav gear for serious offshore cruisers.
