Earth X

Hi Joe,

Your argument is very persuasive and I am inclined to adopt your position.

You should know, several other commentators have stated they charge their Earth X after every short flight/engine run.

The reasoning is:

The engine run time has been too short to bring the battery back up to full charge.

They wish to minimise the high current draw/delivery by the engine charge system, seen immediately after engine start.

I don't know how long it takes to bring the battery up to full charge after running the starter. It's not dangerous to go to 100% on a protected battery like EarthX, but it just reduces its life compared to keeping it between 10 and 90%. It's a bigger deal with cell phones where each little drop in capacity hurts. Also LFP technology (EarthX is LFP) is a little more resistant than LCO or NMC.

Some BMS systems only let a battery charge up to 90% so a 90% SOC (State Of Charge) is 100% full. I don't know if EarthX does that. The manual says 14V (actually "13.9 or higher") is full and divided by 4 cells that is 3.5V per cell. According to Wiki a LFP cell can be charged to 3.65V max so unless the EarthX battery goes up to 14.6V then it isn't "really" 100%. I have no idea what the BMS cut-off is but if it's less than 14.6 then the battery is well protected. Otherwise maybe it just depends on your charge system.

But no matter how you abuse it (charge too high, keep too cold, float at high voltages) it will still lose capacity more SLOWLY than lead acid and lithium batteries will last LONGER! Lithium technology is really great!

So I'm not saying that people should avoid letting their EarthX charge, just that it is not "needed" or desired to top it off as much as possible. It'll still outlast a lead acid battery no matter how you use it. My only gripe with lithium: It's harder to estimate State Of Charge from a voltmeter because the voltage during discharge is not linear. Is 13.2V means you have 80% battery left or 20%? You never know.

My understanding of EarthX technology that the value of maintenance charging on a routine basis with a charger like an Optimate is to be sure that the cells are balanced

Cell balancing is done by the battery management system (BMS) internal to the battery case, regardless of the source of charging current.  For a two-terminal battery like the EarthX (where individual cell voltages are not available on an external connector), there's nothing the charger can do to affect balancing.

If the plane is flown even semi-regularly, and the starter spins with its usual oomph, then there's no benefit to "maintenance charging" a lithium battery.   A normal engine start depletes only a tiny fraction of the stored energy capacity; that energy is very rapidly replaced by the charging system.

Any properly designed LiFePO4 battery charger, including the Optimate, just provides a constant current, then constant voltage charging profile, with the correct upper cutoff voltage for LiFePO4 (max 3.65V per cell).  EarthX probably doesn't push them that hard in the interest of longevity, and in any case, the BMS cuts off charging when it has had enough.

Once charging is complete, lithium-chemistry chargers don't provide a continuous float charge like lead-acid chargers do.  Instead, they may periodically check battery voltage and initiate another charge cycle once the battery self-discharges.

There's no magic to any of this, despite the marketing hype and fear-mongering that battery and charger retailers spread around.  The electronics industry is awash in specialized integrated circuits for battery charging that can handle all of the above, while communicating charge status over a network bus to whatever computer or microcontroller is running the show.