I've inherited a 110v battery pack that used to be used for a solar array made of 34 each 100 amp hour LiFePo4 3.2v for a nominal voltage of 108.8v all together. I'm getting about 90v total from the leads off the pack, so I know that it's severely undercharged. I'd like to take them all apart and diagnose each one to see how they're doing.

What is the correct procedure to safely disconnect each battery from their series set up? Do you need me to supply pictures to better show how the batteries are wired? I'm asking because I've only dealt with 12v Lead Acid Deep Cycle batteries so far, 10.9% of the 110v I'm getting into. If I can safely recycle any of these for another project I'd be elated.

(As for the batteries, the last time they had a full charge was 3 weeks ago, they've probably only been through 300 cycles @ 50% discharge and the reason they're discharged right now is a human error... they were left attached to a DCDC converter :-( )

Thank you all.

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    \$\begingroup\$ Without a photo that says this battery package is really meant for manual servicing, and without you showing that you understand the risks of dealing with something that can easily source hundreds of Amperes: I'd say the procedure is step the hell away from that battery pack. \$\endgroup\$ – Marcus Müller Mar 15 '18 at 22:15
  • \$\begingroup\$ A bit of background: Battery packs, or even individual cells, typically come with protection circuitry that prevents over- and undercharging, and often some things like overheating. No, your "it's severely undercharged" would indicate a lack of such protection. The moment you drop a screwdriver in a bad position, you could be shorting these high-current batteries. Which would mean that not only could you weld your screwdriver to the contacting points by that, but also will these batteries get very hot very quickly. Not a good thing to happen in an array of 34 potentially explosive cells! \$\endgroup\$ – Marcus Müller Mar 15 '18 at 22:33
  • \$\begingroup\$ These are 34 each Winston 100 AH cells. - link for reference only: ev-power.eu/Winston-40Ah-200Ah/… - I'll go grab a picture of them as well to see how they're connected in series. \$\endgroup\$ – Lunchbox Mar 15 '18 at 22:51
  • \$\begingroup\$ Their capacity as well as total voltage is why the first step I'm taking is learning vs doing. They still have potential - a potential safety hazard first - and potential useful life second. \$\endgroup\$ – Lunchbox Mar 15 '18 at 22:53
  • \$\begingroup\$ @MarcusMüller - I'd love to have someone else step in while I step away, but right now I'm the only one that's willing to even tackle the learning curve and safety precautions to take care of these cells in this state. The safest route is just to recharge them, but the charger was set up for 110 and has a safety shut off if the pack shows it's below a certain voltage (the charger thinks that the pack it was programmed for has been altered essentially). Since undervoltage lithium cells present their own problems I'm giving them my full attention to rectify the previous error. \$\endgroup\$ – Lunchbox Mar 15 '18 at 22:58

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