How many years does an HTC phone last?

These things are currently cheap in the bay.

I also feel a significant improvement in the last 2 days

1x battery calibration could also help. But if a new one comes in, I would definitely do it.

Hi, ****** I understand your concerns about the battery life of your Nexus One. The following steps should increase the runtime significantly:
Please connect the phone to the charger while the phone is switched on and let it charge until the LED indicating the charging status is green.
Unplug the phone from the charger and turn it off.
While the phone is still off, reconnect the phone to the charger and let it charge again until the LED turns green.
Unplug it from the charger and turn it on.
As soon as the phone has started up completely, switch it off again and connect it to the charger until the LED lights up green again.
Unplug it from the charger, turn it on, and use it.
You only need to go through this procedure once.

When the battery is fully charged
enter in the phone,
There you can read the mV value of the charged battery. Calibration should be better.
Maybe someone can post values ​​beforehand afterwards.
Is also useful to test a new battery from the bay.