Upgrading Lead-Acids to Lithium

Lithium batteries that are a drop-in replacement for Lead-Acids are the new talk in the RV community. With more useful capacity, built-in protection, and very long life expectancy but on the downside of a higher initial price. When is it making sense to switch?

Better batteries are really only used when not plugged into shore power in an RV park. If all the time not plugged in is spent traveling between parks is the higher price for Lithium batteries not worth it. A set of AGM batteries can easily provide 7 or more years of maintenance free service with the very low daily load on the batteries.

If the RV is often stored and batteries are replaced because of being completely drained and prematurely destroyed Drop-in Lithium can be a solution. The Battery Management System (BMS) built into the Lithium battery ensure that even when no charging is applied for months is the batteries not hurt actually, a Lithium battery not fully charged can be stored for a very long time with minimal degradation also at very low temperatures. So for a travel trailer used seasonally can this be a good solution to avoid buying new batteries every one or two seasons.

So Drop-in Lithium batteries make the most sense when boondocking more than a few weeks a year. It often is the case that a large Class A Motorhome with Lead-Acid battery can sustain the loads for 15-20 hours (to 50% State of Charge) with the batteries possible to fit in the RV. This requires running the generator at least twice a day morning and evening. At least once a day should a full charge be performed, going through both the Bulk and Absorption cycle that add 1.5-2.5 hours to the generator run time compared to just charging the energy used.

A lead-acid battery also has a few charging issues to consider. With a typical setup of four Lead-Acid batteries using 4 x 6 Volt Golf Cart batteries is it only two 12 Volt strings. Manufacturers of Lead-Acid batteries suggest to never charge a battery with more than 20-25 Ampere per battery, this is very important for AGM that if gas is expelled from the vents is the battery capacity reduced and cannot be restored. So maximum charging for four 6 Volt Lead-Acids should be limited to 50 Ampere, many Inverter/Chargers like the Magnum MS2812 have a 120 Ampere charger than then only run at ~40% of maximum load. That extends the runtime for the generator even more.

With Lithium batteries replacing the same physical space can the four AGM Lead-Acid batteries with 50% * 2 * 220 AH = 220 AH useful energy be replaced with 4 * 100 AH = 400 AH useful energy. This allows a Large Class A motorhome that could run 20 hours on the Lead Acid batteries to now do over 24 hours 20 * 400 AH / 220 AH = 36.4 hours. So running the generator once a day is now an option with more than 50% spare capacity from the Lithium. The factor limiting the charge for Lead-Acid also exists for Lithium batteries but is 50 Ampere per battery. So the four 12 Volt Lithium batteries in parallel can be charged with the full 120 Ampere from the charger and still be under the maximum charge limit 4 x 50 Ampere = 200 Ampere.

Comparing the needed run-time for the generator is now possible. The total draw needed is 220 AH * (24 Hours / 20 Hours) = 264 AH for a full day.
Lead-Acid: 264 AH / 50 Ampere + 1.5 Hours = 6.78 Hours
Lithium: 264 AH / 120 Ampere = 2.75 Hours
A thing that has not been considered here is the fact the charging efficiency for a Lead-Acid battery is typical 85% for Lithium is this over 95%. So the amount of energy and time need is even more in the favor of the Lithium batteries. Having a good solar setup can, of course, finish the absorption for the Lead-Acid batteries and also cut down on the required run time of the generator needed for both types of batteries.

Running high loads from a battery system like over 100 Ampere DC is also affecting Lead-Acid more than Lithium batteries. This is called a Peukert Factor and lead-Acid batteries drained at 4 times the load compared to the 20-hour load can often only supply only 160 AH instead of the rated 220 AH.  This does not affect Lithium to the same degree and very little energy is lost based on draining by higher loads. Running a convection oven is a good example where the Lead-Acid batteries are using a lot more State of Charge.

Pricing for initially buying Lithium batteries is the hurdle for cheaper RV's, but for most people with larger and newer Motorhomes is the convenience, generator runtime, stable power, running high loads and ability to run heaters overnight more important. The promise for years of service without degrading batteries that need replacement when wanting to go play is important too. So compared with a solution to use quality Lifeline AGM batteries and Battleborn Lithium and 50% of the time boondocking over a 10 year period. The Lifeline when treated properly provide 1200 cycles, the Battleborn Lithium 3000 cycles. In 10 years with 50% boondocking is 10 * 365 * 50% = 1825 cycles for boondocking and probably 10% more for staying in parks or stored, so around 2000 cycles, requiring at least one replacement of the Lead-Acids batteries.
Initial purchase cost based on Quartzsite show pricing:
Lead-Acid AGMs: 2 x 4 x $350 = $2800
Battleborn Lithium: 1 x 4 x $850 = $3400
This leads to an initial cost advantage to Lead-Acids but now consider generator runtime. With a Diesel full cost of $3 per Gallon and 1/4 gallon per hour during Led-Acid charging and 1/3 a gallon for Lithium based on the higher load on the Generator.
Lead-Acids: 1875 x 6.78 = 12700 Hours, 12700 Hours * 1/4 * $3 = $9500
Lithium: 1875 x 2.75 = 5200 Hours, 5200 Hours * 1/3 * $3 =  $5200

Now look at the 10 year cost is the initial purchase price not that important.
Lead-Acids: $2800 + $9500 = $12300
Lithium: $3400 + $5200 = $8600
The saving is over 40% using the Lithium because the running cost is so much lower, even flooded Lead-Acids is not competitive in the long run. Larger Onan generator also typically needs a larger overhaul every 5000 hours that is not included in these costs.

With a larger solar system can many of the hours from running the generator be reduced, typically 1500 Watt of solar power can generate 4 kWh (4000 wH / 13 Volt = 300 AH) in the winter on a sunny day, enough to replace all the generator run-time if the batteries can last over 24 Hours. Lead-Acids can barely last a day and Lithium can run for a day and a half.