Why is my battery not working?

@juanarturo first check your charger with a multimeter. Make sure it has the proper voltage. Next check the contacts and the charger and the battery. Make sure they are touching well. Sometimes an extra strip of metal between those contacts does help to make a proper connection.

It is possible that this is a battery that has discharged below it's threshold level. Once it discharges below that, it will no longer accept a charge. That is why it can't be "seen" by the charger.

There are ways to try to "wake up" the cells as well as. I am not suggesting that you give this a try. It's a big battery and I'd hate for something to happen, like venting with flame etc.

What I have done for myself in a safe environment, I used a different power supply that I set at the required voltage, connecting the positive and negative from that power supply to the battery. I kept it only connected for a few minutes and made sure it was not overheating and repeated that a couple of times. Once it received the charge the battery went above it's threshold and can then be charged with the appropriate charger.

Batteries like that can also be rebuild. Hardest part on that is always cracking the case so that it can be reused. They do not make it easy:-). If you want to that route, we can probably help with that as well. You would need to know how to solder or even invest in a spot welder (think small, check places like Amazon etc.)

Of course, the safest way is always to replace the battery :-) and discard the old one according to your local recycle guidelines. NO LANDFILL or DUMPSTER! Adding images to an existing question