Collecting the discussion about the A123 cells here in order to keep the forum tidy.
The A123 LiFePO4 batteries at Batteryhookup are currently at $50. With shipping they end up costing $1.29 to $1.69 per cell (depending if you buy one or ten packs).
I did some digging and figured what these were exactly used for: As backup power to write data to persisten storage before shutting down in these devices:
“The VNX8000 uses two 2U dual 2.2KW Li-Ion standby power supplies (SPSs) with
removable battery packs and upgradeable firmware. These SPSs provide battery power to
the SPE and to the first DAE (bus 0, enclosure 0). This battery power allows the storage
processors to de-stage data in-flight to the vault area of the reserved space in the event
of a power failure. Once power is restored to the array, any writes that were de-staged are
reconciled and persisted to the target back-end disks to ensure that no data is lost.”
The fact that they were designed to supply only power for short durataion, and the fat bus bars motivate the thought, that they might be designed for high discharge.
They seem to be spec’d for 2420W (ebay source, EMC data source).
Personally, I think these might be amazing value if we could use them as-is with the BMS and enclosure. But space might be an issue.
With enclosure and BMS removed, they make for great pre-welded building blocks, that just need a charge only BMS be hooked up and are ready to go. They could be fit under a board like @b264 does with his Metroboard LFP batteries, just with a larger enclosure (any ideas?).
They are bulky and don’t have the best energy density, but they have decent power density, can be charged fast and cycled for ever. And I just have a soft spot for LiFePO4 cells in my heart. I might not be the only one:
@deucesdown has experience building with these cells.
Read this post and the links in it if you want to be amazed by how much abuse these cells can handle.