We've been connecting our seldom used phones to the charger anytime we're home.

and we never turn them off, they stay on while charging.

We use (3) seldom used phones for a few years, and only one of the batteries went bad.

Bought replacement battery on eBay ... $1 + $7 shipping.

One should avoid frequent full discharges because this puts additional strain on the battery. Several partial discharges with frequent recharges are better for lithium-ion batteries (which are used in most cell phone applications) than one deep one. Recharging a partially charged lithium-ion does not cause harm because there is no memory (unlike nickel-based batteries).

I always put my phone on the charger at night and my batteries last for years.

My wife puts her phone on the charger after it has run out and has had to replace her battery twice.

My $0.02