To lithium LifePo4 or to not Lithium LifePo4 on a sailboat (LFP part 1)
Disclaimer ! I am not a battery expert nor have I ever played one on TV ! (DYODD : do your own due diligence) so some of the reasoning is quite simplified to keep it easier to follow without going into too much depth , if you want detailed info follow some of the links below and learn as much as you can
Last year , when we were sailing around the Canary Islands with Blue Pearl , we replaced our AGM bank, I already thought about replacing the AGM’s for Lithium batteries , but the cost and logistics made that quite impossible .
After one year of continuous use our ‘new’ AGM’s already show quite the degradation and they won’t take us through the night anymore , even when at anchor ! And now that we are nearing the Panama Canal , closer to some major shipping ports , the feasibility of Lithium / LifePo4 (Lets call it LFP from here on out !) seems to be higher than it was before, shipping from China to Miami is ‘reasonable’ , prices of cells are ‘reasonable’ and replacing AGM’s here on Bonaire (and Curacao, Aruba , Colombia) is quite unreasonable !
The ‘benefits’ of LFP over AGM (lead) batteries , for us as long term sailors away from dock/shore power , are :
LFP : 90% usable Ah’s vs AGM 50/60% , out of a 100Ah LFP you can get 98 usable Ah’s vs 50Ah’s from a 100Ah AGM before it needs to be recharged
AGM’s need to be recharged to ‘full’ (ie 14.4v with only a few amps going in) every few days or they will start to degradate , LFP is happiest when not charged to the max and will not loose capacity , on the contrary , they last longer if you dont recharge them to 100% !
LFP : 99% charge efficiency vs AGM’s 70/80% , if you charge AGM’s with 100Ah , only 70 or 80Ah will be put in storage , with LFP that is 99Ah
LFP : 200Ah 12v weighs around 30Kg vs AGM 60/70Kg
LFP : at least 2000 charge cycles (100% to 0% DOD if you discharge at the maximum allowable discharge current of 1C ) vs AGM 500 (100% to 50% DOD)
As you can see LFP has quite a few advantages over AGM , it also has a few disadvantages , mainly its very sensitive to over charging and sensitive to too deep of a discharge , both will shorten the lifespan of LFP ! (As it does with AGM as well but AGM is not quite as sensitive)
Have a BMS to make sure the LFP bank is charged , monitored and balanced properly
Have 3 separate 12v busses , 1) load bus 2) engine bus 3) charge bus
The BMS needs to be capable of disconnecting the busses separately in case of a problem (ie too deep of a discharge or too high of a charge) , and separately because when a problem occurs you don’t want the BMS to cut off ALL power (that would leave us literally dead in the water)
So taking the above into account and adding up all the costs I thought I decided on this :
1x various switches , fuses , relays , cables etc for safety $500/700 + shipping
All in all : 2500 euro ($2750 USD) for a 600Ah LFP battery bank , not peanuts but considering 500Ah AGM batteries would cost me $2350 here in Bonaire , and I would probably get the same lifespan out of those as before, its not horrendously expensive either as I expect to get at least 4x longer use out of LFP
Well.. as always , ‘not quite’
Investigating further , and more specifically investigating the BMS (battery management system) and the safety features they have , I started reading about the Victron LFP batteries , these have built in BMS’s that communicate with external controllers to show various info like SOC (state of charge) DOD (depth of discharge) cell / battery voltage and also use this communication to shut down chargers , loads etc . All using the industry standard CANbus from the battery to the controller.
Would that mean that I could use the (much cheaper) Chinese LFP batteries with CANbus and connect them to Victron equipment ? A post of the same forum quickly brought an answer that these Chinese LFP’s are 100% compatible with the Victron CANbus ! (So they say!) Wow ! That means I could ‘just’ get a Victron controller , some extra pieces of hardware and enormously simplify the whole set up !
So Rene ! What are you waiting for ? Get these Chinese LFP with CAN bus , add a battery monitor , a control unit , some external BMS and we’re done, sailing into the pacific without a (battery) worry on our minds…
Are you ff’ing kidding me ? I knew of course that none of the ‘OEM’s’ build their own batteries , all LFP cells and batteries come from a handful of Chinese manufacturers and even Victron uses Winston cells, but this is the first time I see mentioned which exact battery these ‘ drop in replacement’ LFP OEM’s use . And aside from the plastic battery case colour it all looks 100% identical !
This threw me off my ‘normal’ thinking and made me question the decision I thought I already made, and was making
If Renogy , and Battleborn, and Firefly and Relion and many others, are using batteries with built in BMS , and boaters buy these batteries and put them in their boats without all the needed safety and protection circuits , and the batteries last quite some time . Why should I go down the DYI route ? Surely sending 3x 200Ah battery to Colombia or Panama is equally costly as sending cells , BMS , parts etc ? Not even talking about the ease of install ?
And how big of a risk is it really with 3 batteries ? , even if 1 decides to go into ‘protect’ mode , the other 2 are still up and running not cutting us off from power immediately ? And since we have good (the recommended) battery chargers , Solar MPPT etc , that can all be accurately and conservatively be adjusted for LFP , what are the risks really ? I could even use 1 of the 3 as ‘spare’ , hook it up , put a battery switch on it and just let it sit there for emergency use only (LFP won’t discharge over time, just put it away with a 30-50% charge)
And should we even be aiming for 2000 cycles ? All the numbers say that if you do the 100% to 0% you get 2000 charge cycles , but what people don’t realize is that after those 2000 cycles you still have 60-70% of the original capacity left ! Which in our case would be 330-360Ah , that is still more than what we would get from a set of brand new AGM’s with a 500Ah total ’stated on the battery’ capacity ! (250-300Ah usable)
I need a beer , sit down .. and think things through
And I need to send some of the Chinese Manufacturers an email asking for a quote for 6x 100Ah, 3x 200Ah , 2x 300Ah LFP’s with CANbus support, LCD panels for charge display and built in BMS’s , lets see what they are offering
Too be continued ………… (really , as I havent made up my mind but would love some input)z