Batteries batteries batteries LiFePo4

Techie with angst…

We went through buyers elation in finding “drop-in” batteries for s/v Hajime.  and ordering them QUICK LIKE so our friends could bring them down to Mexico on their already planned trip…

Buyers remorse, in finding more and more information on “What have we done?” buying the LiFePo4 “drop-in” batteries…

Ordered more and more stuff to support our, already made, decision (no going back now…)  on the set of 4 each 100Ah drop in batteries to make our 400 Ah house bank for the sailing vessel…

STUFF so far…

4 ea LiFePo4 100 Ah batteries, made from 26650 cells 4P31S, LIFEPO4 12V 100AH LITHIUM PHOSPHATE DEEP CYCLE BATTERY FOR SOLAR & WIND SLA Repl

1 ea Solar charge controller, programmable on all charge parameters from 9 to 17 volts , 4215BN EP Tracer 40A 12V 24V MPPT Solar charger Controller regulator with MT50

1 ea Victron battery monitor, Victron Energy Precision Battery Monitor BMV-702S 

2 ea Amp meters with kWh and shunts, just to see what a $17 meter can do… 100A DC Digital Watt KWH Current Power Energy Meter Ammeter Voltmeter 7-100V US

1 ea digital thermometer to help keep an eye on alternator and battery temperatures, Digital Thermometer Dual Channel Input Thermocouple K J T E R S N C/F Type TQ22

2 ea thermocouples with 10 ft. lgth… New Omega 120″ × 0.01″ Fine Wire Glass Type K Thermocouple # SA1XL-K-120-SRTC

1 ea just in case got a diode based charge splitter???, NEW Sealed Sure Power 1202-D Marine Auto RV Battery Isolator 2 Batteries 120 amp

1 ea Added a 150watt solar panel to the house system taking the house solar charge capacity to 420watts, Newpowa 150W Watt 12V Solar Panel High Efficiency Poly Module Rv Marine Boat Off Grid

Installation took a couple days:

We removed the LEAD ACID GC-2 6 volt 220 Ah batteries (4 each) from our battery box under the helm, up through the starboard lazaret hatch. This was the hardest part of the job, the GC-2’s weigh close to 65 pounds a piece for a total of 260 pounds REMOVED.

The new batteries weighed in at  about 27 pounds each for a total of 108 pounds INSTALLED…    The ebay add had them listed at 18 kg or 39.7 pounds each, so we are pleased .

NEW BATTERY SIZE: also smaller than the listing on the Ebay add, the actual size is:

10-7/32″  x  6-3/16″  x  9-5/8 ”     or (260 x 158 x 246) in millimeters 

Two GC-2’s got us spec. 210 Ah at 12.7 volts nominal and two LiFePo4’s have spec of 12.8 volt nominal at 100 Ah each for total of 200 Ah for two…   AND you all know the differences in usable amp hours for the LiFePo4’s vs. lead acid batteries so why go there again?

Interesting stuff found while we were playing with the batteries…

Battery packs  arrives at an average of 13.1 volt state of charge.   We connected the four in parallel and let them sit overnight then disconnected them from each other.  And they were all within 0.02 volt of 13.1 volts at rest for the next couple days …

We hooked up all the new battery monitors and gauges into the boat systems and then, hooked the LiFePo4’s into the boat system.

We applied the shore charger and could only get it to pump around a max of 10 amps from the 25 amp rated Newmar shore charger.   Installed our backup shore charger, a IOTA 30 amp IQ4 system and got similar results.  The system voltage would not get much above 13.5 volts.   Thinking the chargers go to acceptance or float charge directly because of the higher nominal voltage in the LiFePo4’s.

NEED TO WORK ON THE SHORE CHARGE SYSTEM!  At least need to see how it works on a more fully discharged battery bank…

After installing the new 150 watt solar panel to bring the house to 420 watts, and the new 40 amp solar charge controller, we found we could get about 150 total Amp Hours pumped into the batteries and called them full at a system voltage during charging of about 13.88 volts.

This FULL matched the shore charge FULL and the new solar charger turns charging off at this voltage, we programmed it to do so…

On to the alternator.  This morning, we ran the engine to study the alternator charge system.  The house was at  -50 Ah from full on the system’s new Victron BMV-702 battery monitor.  We ran for 1.25 hours and monitored the alternator temperature and power and energy and voltages.

The engine running for 1.25 hours pumped the 50 Ah back into the batteries max observed amperage output from our 120 amp alternator was 50 amps.  Max alternator temperature observed was 180 deg. F.   When the battery bank was full again, we manually re-directed the alternator output over to the starter battery to assure ourselves that the alternator would drop down to nominal output amps.  ALL WORKED AS PLANNED…

Next steps are to live off the batteries only for a bit at dock and run them down to 20% SOC (state of charge) and then see what it takes them to charge up again…

Wish us continuing persistence…

Some new battery photos…

New Boat Electrical Schematic:

Hajime Battery 2



FIN for now…



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2 Responses to Batteries batteries batteries LiFePo4

  1. Allen says:

    Wow, taking them down to 20% SOC? Those batteries can handle that? Over what time period or how often can they be discharged to that level?

    I have AGM batteries for my PV system, strung in series parallel to get a nominal 48 v system. It was not recommended to take them below 50.4 v or 12.6 v per battery. This represents 90% SOC.

    Allen Gordon Sent from my iPad


    • svhajime says:

      Here is a link to a lovely 3 page rant on LiFePo4 Batteries for marine use:
      More than you want, maybe, but he covers all your points pretty well. Nominal 100% charge on a LiFePo4 battery built for 12 VDC is 13.88 volts. Cells at rest should be 12.8 VDC in a nomial 12V system. They pretty much run all day from 13.88V to 13.2V (from 100% SOC down to 20%). He has a lovely graph on page 3 of blog and page one is the differences between Lithium and lead acid discussion… Jim

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