Hoover handheld vac, needs battery (Fremont-Sundale/28 Palms)

Hoover 300 series cordless wet-dry handheld vacuum. With all accessories (charger, wall mount, wet nozzle and crevice nozzle).
Needs a new battery. I have already replaced the battery once. You can find replacement NiCd batteries online for ~$25.
The charger tends to overcharge the battery if you leave it plugged in. And NiCd batteries self-discharge over time if you don't plug it in.
This vacuum works best if you use it frequently, which we don't. So we end up either wearing down the battery by overcharging or leaving it out of the charger and then not having a charge when we need it.