With LFPโs youโd be better off to just leave them in continuous parallel, no longer a need to isolate oneโฆ
Charge them both to 100% before putting them in parallelโฆ
I will add here what Iโd penned in another thread awhile back, but take note of item #2, because determining state of charge (SOC) with LFP is problematic due to itโs relatively FLAT discharge curve (meaning relatively near-stable voltage):
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Well, since (your camper) spends much of itโs life plugged in, you might then consider doing what I and many others with LFPโs doโฆ
1) Simply add an automotive โside-postโ battery knife style disconnect switch to the LFPโs two terminals (the most accessible), so that the battery can hibernate isolated when not in useโฆOnce isolated, the self-discharge rate for LFPโs is practically non-existent, say over a 6 month period. Hibernation should be done with the battery at about 50-60โish% state of charge (SOC), this to keep LFP ions in appropriate equilibriumโฆ
2) To best determine โaccurateโ SOCโs with LFPโs (otherwise somewhat problematic), youโll want a good LFP compatible, shunt based SOC meter, like Victronโs โsmart-shuntโ with Bluetooth (simply installs in NEG battery cable)โฆReads like a gas gauge and provides SOC, volts, amps and historyโฆ
3) With battery disconnect during these periods of โnon-useโ, your existing on-board converter-charger (via shore power) will take over and continue to supply 12v power to the camperโฆ
4) When restoring your batteries back to a full charge, most any OEM charger thatโll output 14.X volts (not to exceed 14.6v) will do - however, the key here is, once the batteries are fully charged and *balanced (say, another 15-20 mins after achieving 100% SOCโฆ), discontinue charging (this, in the interest of battery longevity), by shutting off your generator (or if shore power, via on-board converter-chargerโs breaker), thereafter running off battery powerโฆ
* Note, the cell balancing cycle can be observed via Bluetooth per the slight cycling of amps and volts until such cycling stops (see item 2).
5) Unlike wet-cells, thereโs no need to โroutinelyโ restore LFPโs back to a 100% FULL chargeโฆ85-95% is quite sufficient thanks to LFPโs far deeper DOD (depth of discharge) - But to aid with battery longevity, youโll only want to do a FULL charge occasionally, and for just two reasons:
a) Periodic cell re-balancing (this process begins after achieving 100% FULL Charge).
b) Meter resync (concurrent with a full charge) - to resolve cumulative SOC meter drift which naturally develops over a timeโฆ
6) At this point you might sense (as with other type batteries) that solar harvest will help minimize the frequency for having to run your generator, as does LFPโs deeper DODโฆ
3 tons
