in praise of the single Battle Born lithium battery

I have ranted elsewhere that buying too much lithium battery bank is a self-limiting behavior due to prohibitive cost.    I may have been wrong – I have seen lots of people running (or planning to run) multiple Battle Born batteries at $1000 per BB.

Holy crap, y’all.  That’s real money.

Yes, I think a BB is worth $1000.  The question is whether or not that second (or third or fourth) one is worth $1000:

...economists sometimes speak of a **law of diminishing marginal utility**, meaning that the first [unit](https://en.wikipedia.org/wiki/Units_of_measurement) of consumption of a good or service yields more utility than the second and subsequent units, with a continuing reduction for greater amounts...  -- [wiki article on marginal utility](https://en.wikipedia.org/wiki/Marginal_utility)

Yes, there are edge cases where people will need multiple BB (running A/C at night or something) but normal folks in normal vans might be better off with just one and keeping the other $1000[s] in their wallet.  Or off the credit card balance.

Here’s my reasoning:

  • lithium has huge current throughput.  1C (100A per 100Ah of capacity) is pretty common.  This means the banks can take charges quickly and runs heavy loads that would take more AGM (and way more flooded) to cover.

  • lithium charges linearly with no special time contraints .  None of this long duration absorption that Pb requires.  You can charge in small bursts with no problem.   Locations or seasons with low insolation are much less problematic when the bank can greedily suck up whatever is available.

  • 4S LiFePO4 banks are fully charged at 13.8v (and 3S non-LFP li-po even lower);  they don’t need high voltage charging like lead chemistries do.  This means regular alternator charging will work fine.   It also means the solar charge controller can be set to a lower voltage – mppt controllers will put more current into the bank at lower [quasi-absorption] voltages.   Example:  BB recommends charging at 14.4v, probably to keep current moving into the battery and provide enough overvoltage for top-balancing the cells.   If your MPPT can put out 200w it will make 13.89A for the bank at 14.4v instead of 13.51A @ 14.8v.  A small difference, but moah powah is moah powah.

  • Lithium capacity is usually stated as 2x lead capacity since lead is typically depleted down to 50%.   This leaves out charging efficiency - lithium charging is practically perfect while lead carries a 10-30% charging inefficiency (my own rough calcs suggest 13%).   I suspect that practically speaking (due to the charging characteristics of Li) BB capacity is more like 3x greater than rated lead capacity.  Note:  Firefly, makers of the BB, warrant the battery even when used from 0% to 100% state of charge.  So run the snot out of them.  People building their own packs (especially w/out BMS) might be better off using the “middle 80%” with occasional top-balancing, and thinking of those banks as providing 2x lead capacity.

  • smaller Lithium banks are easier on stock alternators

unsolicited advice to folks in the planning stages

Give serious consideration to building your rig around a single 100Ah BB battery.  If the power calculators suggest you need more than than that:

  • think about moving heavy loads to daylight hours (running them off the panel)

  • think about taking half (or a quarter) of the money of that 2nd BB and buy more panel

  • think about moving heavy loads like cooking and heating to propane or other fuel

  • and in general stop thinking of your van like it’s an apartment – you are the power company and you will make every watt you consume

Updated:

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