The False Economy of Cheap Lithium Batteries
Our last post compared the cost per kWh per year of lead-acid batteries against that of lithium iron phosphate (LFP) batteries. LFP chemistries came out as the obvious winner. But there is some fine print you should know before scooping up some “good deals” from Amazon or some rando suppliers.
The problems with cheap lithium batteries
We took apart and tested a mid-range (or not-bottom-of-the-barrel) LFP battery available on Amazon. The build is pretty clean without any glaring safety concerns. But we uncovered a few issues:
The inside of an LFP battery pack from Amazon.
The discharge setting is too aggressive
Aggressive discharge means a shorter lifespan for any battery chemistry. That’s physics, yo.
The cells in the Amazon battery we tested are configured to discharge very aggressively. The setting allows the pack to achieve the stated power storage capacity with fewer cells, reducing production costs and increasing the profit margin at the customer's expense.
While most Amazon listings promise anywhere from 4,000 to 15,000 lifecycles, the reality would be much closer to 300 (if that) because of the aggressive discharge setting (sometimes over 98%). As a comparison, we set most of our LFP batteries to discharge only down to 80% to balance performance and longevity.
No protective thermal circuitry
LFP cells cannot charge below ~33 degrees Fahrenheit or discharge under -22 degrees Fahrenheit. If you charge them when the ambient temperature drops below ~33 degrees Fahrenheit, the cells die. Period.
High-quality LFP batteries (e.g., our custom-built packs) have protective circuitry to prevent the cells from charging when the ambient temperature is below ~33 degrees. However, adding the feature is an extra cost that sellers who compete on price, not quality, don’t want to bear.
The Amazon batteries we tested are explicitly indicated for indoor use to ensure they’re stored and used at room temperature. Based on the instructions and the charging temperature specified on the datasheet, it’s safe to assume that these batteries don’t have the appropriate protective circuitry to prevent them from charging in a below-freezing environment.
If you house your off-grid solar setup in a shed or a cabinet outside the house without proper insulation, there is a non-zero chance that the ambient temperature will drop below ~33 degrees when the battery charges. The condition would kill the LFP cells instantly.
(Note: We solve this issue with our proprietary cold temperature-tolerant custom battery pack.)
Fly-by-night brands with no reputation
These cheapo LFP batteries actually perform quite well out of the box and may last ~3 years without obvious problems. That’s when the “extended warranty” expires, and the fly-by-night brand is long gone — giving you no recourse to complain, let alone get your money back.
Lithium-ion batteries are assets, unlike alkaline or lead-acid batteries, which we treat as consumables. With the appropriate configurations and operating environments, LFP batteries last as long as, say, a vehicle (which is also considered an asset).
Fly-by-night brands on Amazon have no incentive to ensure their products work 5, 7, or 10 years. Their incentive is to maximize profit by building products that meet the specs and work for the next 2 or 3 years. Then, they don’t care.
5-star reviews posted right after a customer receives the product saying, “This thing works,” means nothing. Youtube reviews stating they “actually meet their specs” don’t either. By the time the battery breaks, the listing is probably long gone.
We treat our batteries like royalties (and we talk to them)
Our custom battery packs don’t aim for the lowest price tag. Instead, we help our customers achieve the lowest cost of ownership over the battery’s entire lifespan.
With the appropriate configurations and setup, LFP batteries can last as long as 10 years, if not more. For example, we use advanced battery management systems (BMSs) to set characteristics like discharge depth, and we 3-D print custom braces that allow us to apply the appropriate pressure to the battery pack to optimize performance and longevity.
Yep, there’s a lot of battery whispering going on here :)
