Paul makes some good points but I want to remind everyone that there is no such thing as a drop in replacement lithium battery for boats. Accommodations must be made on the charge side. Charge profiles need to be 3 stage and specific to lithium chemistries. Also, you can do serious damage to your alternator if you try hooking up a large lithium bank to a small alternator. The internal resistance of lithium cells is so low, the alternator will quickly burn out trying to supply the load. Additionally, the drop in replacement type batteries pose an additional hazard in that a high voltage disconnect would also destroy your alternator if precautions are not taken.
One last gripe, the YouTuber, Will Prowse, is a hack. He is not an engineer, nor an expert on lithium batteries. He is an expert in online marketing. His business model is to promote the cheapest of products with affiliate links so he gets a kickback of anything he mentions. People always want cheap, and are fooled into believing they're getting cheap and great when someone on the internet purports to be an expert. On Thu, May 26, 2022, 3:24 PM Dreuge via CnC-List <cnc-list@cnc-list.com> wrote: > Dave, > > As I mentioned in previously replies to the list, it no longer makes any > sense to buy lead acid batteries(i.e. flooded, gel, or AGM) for a house > bank. For lead acid, the AH capacity is highly dependent on the current > load due to the Peukert Effect. Deep cycle lead acid batteries are rated > at C/20. For a 100AH rated battery, this is 100AH/20H = 5A. This is > often called the 20H rate, i.e. 5A * 20H = 100AH. If the actual load > is 20A, then the same 100AH rated lead acid battery would only provide 60AH > (or 10AH at 100A). And worse, one should only use 50% of a lead acid > battery’s capacity as going below 50% substantially degrades the battery > lifetime. This means that a 100AH lead acid battery has an effective 50AH > @ 5A (or 30AH @ 20A). > > Let’s assume a 100AH lead acid battery price of $264 (the average of the > Amazon prices), then 2 batteries would cost one $528 and one would get an > effective 100AH (50%*200AH) at 5A loads. > > Now, the price of LiFePO4 batteries have come way down in the last few > years and their performance and lifetimes are a magnitude better. A 100AH > LiFePO4 battery is typically rated at 1C. That is they can deliver 100AH > at 100A for 1H(or 5A at 20H or 20A at 5H). They can also charge at amps up > to 100A which is impossible for a lead acid battery. And LiFePO4 > batteries live 5 times longer. That is, one would expect to replace 5 > sets of lead acid batteries before replacing a LiFePO4 battery. Yes, > LiFePO4 batteries are more complex as they require a battery management > system (i.e. BMS), but there are companies which provide 12V drop in > replacements with the BMS built internal to the battery. Top companies > like Battle Born sell a 100AH LiFePO4 for $874 and provide a 10yr warranty. > Renogy sells a 100AH LiFePO4 for $765. A company, CurrentConnected.com, > sells > a SOK 100AH LiFePO4 battery for $569 and it has a 10 yr warranty! > YouTuber Will Prowse rates the SOK as the best value LiFePO4 12V drop in > replacement (see https://www.mobile-solarpower.com/lithium-batteries.html). > There are a plethora of cheaper 100AH LiFePO4 batteries that can be found > on Amazon, Ebay, AliExpres, …, but one gets little service and limited > warrantees, so I would recommend avoiding these. > > Rather than buying 2 100AH lead acid batteries for $528 at a total weight > of 140lbs(70lbs each) , one could just buy 1 100AH LiFePO4 for $569 > weighing only 28lbs and get a better performing battery. That is basically > the same price. If one takes into account the increased lifetime, the > saving is HUGE! > > If one builds their own DIY LiFePO4 battery, the savings is much much > greater. Last year I replaced 2 100AH lead acid batteries with one DIY > 560AH LiFePO4 battery for a little over $900 (see my blog link below). The > DIY LiFePO4 battery occupies the same location and physical space as the > previous 2 lead acid batteries, it weighs much less (95 lbs vs 125 lbs), > but has 5 TIMES the capacity. > > I recently gave a talk on off-grid solar systems a local amateur radio > society meeting. The discuss the battery as the heart of the system and > make the case for LiFePO4 batteries. My slides from the talk are available > on my blog: > > https://svjohannarose.blogspot.com/2021/10/solar-off-grid-system.html > > > Also, the details of my DIY 560AH LiFePO4 are posted at the link below > which includes details about alternator charging. > > > https://svjohannarose.blogspot.com/2021/06/adding-new-lifepo4-to-house-battery.html > > > > > > - > Paul E. > 1981 C&C Landfall 38 > S/V Johanna Rose > Fort Walton Beach, FL > > http://svjohannarose.blogspot.com/ > > On May 26, 2022, at 11:24 AM, David Knecht via CnC-List < > cnc-list@cnc-list.com> wrote: > > I have been following the battery discussion and have a question. I need > to replace my two 9 year old AGM batteries this season. I have separate > start and house batteries which can be combined if needed. I don’t have > large power needs (electronics, autopilot and fridge when cruising). I > have been reading and researching this and I am unsure of what to > purchase. From what I have read, AH is the important number to focus on. > Last time, I got Lifeline AGM group 27 from Defender. Defender has 3 > different group 27 batteries > Powertech rated at 92AH which cost about $330 > Lifeline rated at 100AH for 432 > Northstar rated at 92AH for 457 > > From Amazon, I can get a VMAX group 27 with 100AH for $289 or a Universal > with 110 AH for $239. Is there any reason to be concerned about less known > (to me) brands from Amazon or does it make sense to just focus on the > numbers? Thanks- Dave > > S/V Aries > 1990 C&C 34+ > New London, CT > > <pastedGraphic.tiff> > > >
