backchannel The Best RV Battery For Boondocking

contra lithium

Saw this link posted on twitter and wanted to address the rampant misinformation. I will be gracious and assume the author is a general-topic freelancer and was handed an assignment.

Full disclosure: I have used both lead-acid and LiFePO4 for boondocking.

first things first

There is no “best RV battery for Boondocking”; there may be a best battery1 for a specific use case.

Before proceeding you may want to reflect upon my theory regarding the hierarchy of bullshit

first paragraph

RV boondocking demands 12 volt, 100 amp hour deep cycle RV batteries that charge up quickly from solar panels and are able to handle discharge rates of 80-100% of their capacity.

Boondocking requires zero of the things in that list. The author is tipping their hand about what they want The Answer to be.

Boondockers frequently require more power than a single battery can provide,

Number of batteries is irrelevant.

especially if they use AC appliances such as coffee pots, blenders, TVs, or AC power outlets in addition to DC power (lights, pump, furnace).

That’s choose, not require.

If you plan to boondock for a number of days, or even weeks using solar panels to recharge your batteries, you’ll probably want more than two batteries to store power

Why the fixation on number of batteries?

and keep you powered even on cloudy days

Probably cheaper to overpanel or have a small generator. Run the numbers to see what works for any given scenario.

Why Lead Acid Is Not The Best RV Battery For Boondockers

They don’t meet the discharge and recharge requirements of many boondockers.

This is a function of Pb chemistry and capacity. An AGM will move a lot of current.

Flooded and AGM lead-acid batteries require ventilation.

The author should probably read up on the literal hazmat that can come out of venting LiFePO4.

Some lead-acid batteries require maintenance.

Some Lithium can catch on fire and burn your RV to the ground.

Lead-acid batteries are about 70 lbs each. Multiple lead-acid RV batteries compose significant weight. This additional weight will be reflected in a significant decrease in fuel economy.

Let’s use a 2x100Ah as an example.

  • battle born 100Ah 31lb. 2x = 62lbs
  • Trojan 100Ah 68lbs. 2x = 136lbs
  • 136lbs - 62lbs = 72lbs

Does the author really believe that 72lbs will result in a “significant decrese in fuel economy”? 72lbs is what ~8 1/2 gallons of water weighs.

flooded lead-acid batteries contain lead plates that must remain covered in sulfuric acid. This requires them to be topped up with distilled water at least every 2-6 weeks.

Right. Also, your RV gas tank must remain stocked with fuel every 2-6 weeks.

Flooded lead-acid batteries will be permanently damaged if they are discharged by more than 50% of their capacity.

No, it doesn’t work that way. If you want to know how DoD affects lifetime cycles consult your battery’s DoD vs Cycles curve.

further reading

Even at just 50% capacity, It takes a flooded cell battery about 8 hours to recharge.

It takes 5-6hrs for any charging rate between the max and min rates.

Flooded cell batteries weigh a hefty 70 lbs, so they add significant weight to the RV.

See above.

AGM Lead Acid Batteries

AGM batteries are better than flooded cell lead-acid batteries for RV applications as they can be discharged up to 80% of their capacity.

No they aren’t, and the DoD vs Cycles curves for AGM and FLA are virtually identical. AGM does not possess magical abilities to tolerate deep discharge without damage.

These lead-acid batteries recharge up to 5 times faster than flooded lead-acid batteries.

Incorrect. AGM and FLA require the ~same amount of time to fully charge. AGM will accept more current in Bulk and early Absorption, but the overall time required is the same as Absorption duration will be extended.

AGM batteries have a lifespan of about 300-800 charge-discharge cycles, depending on how much they are discharged each time.

Real deep cycle lead batteries are typically rated to 1000+ cycles to 50% DoD.

Why Lithium Is The Best RV Battery For Boondocking

Lithium LifePO4 Batteries are by far the best RV battery for boondockers.

Even boondockers who camp in freezing weather? Even for boondockers who plan to use the rig for, say, 2 years? As Thomas Sowell said, “There are no solutions. There are only trade-offs.”

Lithium iron phosphate batteries can handle 3000-5000 cycles of charging and discharging before they start to lose capacity.

LiFePO4 are typically rated 2000-3000 cycles to 80% DOD, at C/5 charging rates, after which 80% of rated capacity will remain.

By comparison, a lead-acid battery will lose about 25% of it’s capacity after just 200-500 charge/discharge cycles.

No, they won’t. See above.

Lithium RV batteries can be discharged 100% over and over again with no decrease in battery capacity.

Incorrect. Discharging to 100% DoD2 is harmful to LFP. It’s such a factor in cyclic degradation that manufacturers who allow this customer behavior actually under-rate battery capacity to keep Joe Sixpack from trashing the battery (100% DoD really ~95% DoD). Lead manufacturers could do the same so they could publish better cycle stats at any given apparent DoD.

There is nothing inside LifePO4 lithium batteries to leak out or vaporize, so they can be stored anywhere.

Q. why are there safety vents if there is nothing to leak out or vaporize?

further reading

Lithium RV batteries are the lightest battery option for RV boondockers.

LiFePO4 are the heaviest lithium (Wh/kg). Why not use the lightest, Li-NMC? Don’t want fires? There’s that pesky trade-off concept again.

The Downside of Lithium Batteries

The biggest drawback of lithium batteries for RV boondockers has been their relatively high price.

And irreparable/immediate damage when charged below freezing.

How Can Lithium Batteries Be The Most Economical?

The thing to keep in mind is that over the long run, lithium batteries are a much more economical option than lead-acid batteries.

Long-term costs of FLA (Trojan T015) and LiFePO4 (Battle Born) are very close in $/kWh delivered, with the FLA being slightly cheaper. AGM costs ~2x as much than either of them, but I never claimed AGM was good for boondockers.

Lithium can be the most economical if

  1. the boondocker boondocks long enough to exceed FLA cost (like 14 years?)
  2. without prematurely killing the battery (like <5000 cycles)

Joe Sixpack isn’t going to reach 5,000 cycles because he doesn’t care about it and doesn’t do the homework. Joe Sixpack will likely make it through the warranty period.

I encourage everyone to do the math for their own use case.


twitter comment thread for this post

  1. Even that language makes me squirm. Best fit or reasonable tradeoff are closer to what I mean here. 

  2. or charging to 100% SoC