Ok, if you can, re-read your DMM's user guide. Otherwise, the Internet has basic DMM user guides that can help refresh your memory.

Next, disconnect the battery from the wiring harness/controller and carefully check the batt. output voltage with the meter range set to next highest DC voltage scale above 24v. Be extra careful not to short the meter probes across the battery terminals. If the DMM reads " - 0 " or negative voltage then swap the probes around.

Note: As a safety precaution, the battery charger will not charge the batt. if the voltage reads below a certain level.

Your 24V LiFePO4 batt. has 8 cells.

Each cell has a working (average) voltage of 3.0 -3.3.

Generally speaking, the absolute minimum cell voltage is ~ 2.5V (max is 3.8 - 4.3V).

So, your battery should, at all times, indicate a charge of no less than 20 volts (8 cells x 2.5V = 20 volts).

A battery reading of less than 20V would indicate one, or more, bad cells. Bad cells can sometimes be replaced with new/good cells. However, it's often better to just replace the entire battery.

If the battery checks out, then test the charger output voltage. The DC output for your battery charger should be ~ 30.0 volts.

Note: Ping is a well regarded e-bike battery company that, IIRC, offers well made 24V LiFePO4 batteries at a good price (not sure if they have 30ah capacities tho). Ping is also known for having very good customer service.

Another recommended e-bike battery retailer would be "GoCarLite" (Doug, the owner, is a great guy to deal with).