Dakota LiFePO4 deep cycle batteries - a viable alternative to Lithium ion packs

[j.b.shirk@gmail.com]

The Facebook algorithm has got it in its head that I am in the market for a solar power wall and so keeps feeding me ads for LiFePO4 batteries. Except that none of the ones made for RV solar can be adapted to a 52V e-bike. Then I discovered one made by Dakota that seems viable. I have done a comparison of this against standard Lithium packs and share my findings:

I really wanted to find a way to use LiFePO because I'm not thrilled with the service life of lithium batteries. Without spitting hairs about YMMV use and abuse, let's compare the warranty life as a baseline. Lithium packs typically have a warranty of one year, whereas Dakota LiFePO4 batteries have a warranty of 11 years.

One Dakota model in particular stood out as unique in that its recommended maximum charge is 14.4V, which means 4 units can make a 52V system in series.

Comparison results by Charge capacity (21-25 Ah):

The Dakota is about 66% heavier, by similar charge capacity, meaning its specific energy is about 62% of the lithium packs. It is about 5% more expensive in up-front cost.

However, given the service life of 10+ years, it is about 11% the cost, amortized over 11 year warranty period.

Type	AVERAGE of Charge capacity	AVERAGE of Price tot	MEDIAN of Weight tot	MEDIAN of Specific energy	MEDIAN of Cost/Energy	MEDIAN of Cost/service life
https://dakotalithium.com/product/da...fepo4-battery/	23	916	25.6	101.2	$0.78	$0.07
https://booant.com/collections/52v-t...39557397807167	25	836	15.4	182.9	$0.65	$0.65
https://lunacycle.com/52v-luna-direwolf-ebike-battery/	21	795	14.5	163.1	$0.74	$0.74
Average or Median	23	849	15.4	163.1	$0.74	$0.65
Dakota % of median			166%	62%	105%	11%

Other considerations:

LiFePO4 requires a charger specific to this chemistry
A switching circuit is needed to connect batteries to the load in series, but to charger in parallel. I have not found a 52V LiFePO charger.

No disrespect to Luna packs intended (I only compared models that are no longer available). The BOOANT models were randomly found and taken as representative of high-end, Chinese made systems.

[AZguy]

There's good reasons you seldom see LiFePO₄ in electric bikes - for a given energy capacity they are quite a bit heavier and larger than what is typically used

[j.b.shirk@gmail.com]

I for one, will gladly carry an extra 10 pounds to get up to another 10 years out of the battery - and not throw $600-$800 epoxy-encased lithium packs in the land fill every year and a half. And 1.5 years is really pushing it in terms of useful range.

[AZguy]

I'm still running batteries that are six years old - in that six years I've turned over 10,000mi albeit that's more than one battery... the oldest has seen close to half that though... It's still works fine albeit about 10% less total capacity and higher ESR (more voltage sag) particularly when it's at lower state-of-charge

Again, there are good reasons you seldom see LiFePO4 in electric bikes

The build's I've seen where they made sense [at least to me] was big heavy trikes where the weight and size didn't hurt

LiFePO4 makes good sense for larger vehicles but even then not as the motive power source, just for auxiliary power - there are good reasons you seldom see LiFePO4 in *any* electric vehicle application as the motive power source


I look at it this way... For my use case, I ride a lot but it's not like I'm doing long commutes on a daily basis, I will likely easily get more than ten years from my batteries and at ten years with the Li-ion chemistries I'm using the batteries available at the ten year point will have enough more energy density that it will be a good time to make a new investment... changing to LiFePO4 would be going exactly the opposite way (much less energy density)

And I care about ten pounds, especially for off-road MTB riding... that's where I use a light powerful battery (3.2kg, 14s4p, ~700Wh) that I've had for about five years... That battery mostly gets used when I'm really looking for lowest weight/highest range and is likely to last a very long time - even though I've had it for five years it's only seen a bit more than 1000mi and is pretty much as fresh as the day I bought it five years ago...

[Circuitsmith]

Back when I ran a Currie USPD with LIPO batteries I got about 3 years & 3000 miles before ESR increased about 50%, time to replace cells.
I think key to getting good life was limiting charge to 4.0V per cell except for full charge and balancing 2-3X per year.

I'm using some M-size LiFePO4 cells 4s2p on an overnight (every couple months) battery charger for my infrequently used car.