Battery not holding charge

There are a few possibilities here.

1. Broken charge connector: If the connector has been handled poorly, it may no longer allow a connection between the cable and the device. This usually means soldering a new connector on to the board. They are quite tiny.

You can also attempt to clean the connector with some contact cleaner, which is pretty cheap at any hardware store. Failing that, youc an use isopropyl alcohol and a tiny coffee stir-stick or other tiny implement. Wrap it with some paper towel, soak it in isopropyl alcohol and rub the connector carefully. CAREFULLY.

2. Battery has been allowed to fully discharge past its zero point: This can happen if it has been left discharged for an extended period of time.

In this scenario it is completely unsafe to charge the battery. Copper shunts may have formed a short circuit within the battery. It would light on fire if charged. The battery will refuse to charge itself. (Tiny IC should prevent charging.)

Those are the likely scenarios I can think of.

Since there is no information in this question AT ALL, I suggest you take some pictures or provide a more thorough description, then we can help further.