Root cause 1: High self-discharge, which causes low voltage. Solution: Charge the bare lithium battery directly using the charger with over-voltage protection, but do not use universal charge. It could be quite dangerous. Root cause 2: Uneven current.
If the voltage is below 2V, the internal structure of lithium battery will be damaged, and the battery life will be affected. Root cause 1: High self-discharge, which causes low voltage. Solution: Charge the bare lithium battery directly using the charger with over-voltage protection, but do not use universal charge. It could be quite dangerous.
If you want to charge the batteries up to 2V, maybe set the voltage to 2V then so it stops the current once it reaches those 2V. Be wary though: if the battery voltage recovers on its own to higher than the set voltage, the PSU will be forced to sink current, which most don't support.
Check the voltage and amperage requirements of your battery and compare them with your charger’s output. Using a charger with too high voltage can damage the battery, while too low won’t charge it effectively. Recalibrating your lithium battery can help if it’s not charging to its full capacity.
Lithium-ion batteries are great and all, but they aren't perfect. Just like any other battery technology, lithium-ion battery cells eventually break down and begin to no longer function at their specified ratings. If you want to know how to identify and fix a broken battery, here are some general guidelines.
Always use a charger that conforms to the specifications of your battery pack. This means if you have a 36-volt lithium-ion battery that needs a 42V charge voltage, don’t attempt to charge that battery with a higher voltage battery hoping that the BMS cuts off the charge.