Buying Used LiFePo4 batteries

Purchasing Pre-owned LiFePo4 Batteries

I'm in search of resources concerning the purchase of used LiFePo4 batteries and determining their condition prior to buying. A local seller on Craigslist has 130AH Valence XP U27-12XP Series Batteries that were charged but never utilized as part of a UPS electric prototype vehicle.

The seller is asking $650 each, with discounts for multiple units, which seems fair for 130AH if they are in good working order.

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Below is an extensive account of my experience with these batteries. To sum it up quickly: even with substantial use, they are robust batteries capable of lasting decades. They are highly advanced and can accomplish things you may not be aware of.

Personal Experience with U27-12XP Batteries

I purchased hundreds of the U27-12XP batteries with similar backgrounds to the ones you're considering. By connecting the communication cable to my laptop, I could retrieve a lot of valuable data from the batteries’ onboard computers. Given the electric vehicle's high demand and lack of cooling systems like those in Tesla, the wear was evident. After just 500 cycles, their capacity was reduced to 85% of the original rating. They experienced surges of up to 300 amps and a peak charge rate of 166 amps, with the entire truck consuming 125,000 Watts, equivalent to 160 horsepower.

Application in Solar Systems

Currently, these batteries are part of a solar setup and will undergo light use with shallow cycles. I anticipate that the manufacturer’s discharge curve will remain accurate under these conditions. This means I expect to use them for over a decade, possibly two. Prior to purchasing a large quantity, I conducted numerous tests and found them to be highly impressive. The batteries are well-matched, and there are aftermarket BMS systems available to maintain this balance. Each battery features its own internal MOSFET. If the master BMS determines that one battery should be excluded, it can essentially turn off its cells.

Additionally, if one battery's capacity is lower than the others, the master BMS will adjust its output to ensure all batteries deplete at the same time. This adaptability makes them very versatile, especially for higher voltage solar systems, which are generally tolerant of such changes.

Different Versions and BMS Requirements

Valence offers various versions. One doesn't require a master BMS and has built-in high and low voltage disconnects for safety and battery protection. However, it has limitations in series-parallel setups, making it more suitable for small solar systems. For the model you mentioned, you will need a master BMS or, at least, a module balancer. Larger battery banks benefit more from a $500 BMS.

Ensure your charge controller and inverter know when to stop or else you might need a battery capacity meter with relay controls and a high current relay for protection. These batteries lack internal voltage protection.

Reviving Deemed Bad Batteries

A friend using hundreds of these batteries buys those classified as bad by distributors. Even if they are nearly at zero volts, he revives them gradually and has found their capacity still sufficient. He has assembled a massive battery bank with varying ages, capacities, and voltages, working efficiently for years — something unachievable with lead-acid batteries.

Assessing Battery Condition

To determine if the batteries are in good condition, ensure they haven't dropped to dangerously low voltages. The voltage alone won't indicate their capacity or performance. Assess the remaining capacity based on past use. If you can charge them with substantial amps without significant voltage spikes and discharge without major voltage drops, they should be fine.

For more details, refer to The Benefits of Using lithium ion battery 50ah and What are benefits of Lead Acid Battery for Austria?.

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Acquiring LiFePo4 Batteries from Alibaba or Aliexpress

I used ABBA logistics for customs work since they received the paperwork. You could save around $100 by shopping around, but handling the paperwork yourself might not be worth the effort.

I collected the batteries from a warehouse, saving on local delivery charges. They were easy to transport, considering their 200kg weight. Some cells had minor scratches on their outer covers, which I think are insignificant.

Total Cost Breakdown

Australian $:

• $4,471 for 45 x Prismatic Lithium REPT 230Ah 3.2v LiFePo4 Cells (US$68 each)
• $362 Alibaba credit card fee
• $268 DAT Shipping by Seller
• $115 Port Charge
• $152 Bunker Charge
• $48 Currency Adjustment
• $210 Customs Agent (ABBA Logistics)
• $145 Quarantine Fee
• $45 Document fee (ABBA Logistics)
• $200 Other fees (ABBA Logistics)
• $530 GST
• $6,621 Total (AU$147 each, about US$102 each)

Shipping was handled by the seller as DAT (Delivered at Terminal) to Sydney/Botany. I managed local charges, and the batteries were securely boxed, arriving in great condition.

I charged two batteries and tested them using a discharge tester. They performed better than expected, with a capacity slightly higher than advertised. I plan to top-balance them in the vehicle and address any problematic cells manually.

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