My roomba is not charging! Anyway to fix this?

I’ve tried cleaning the contacts, manually holding the roomba to the charging connections, Using a new charger, using a new battery.

The charger is only outputting 1.6V when the roomba is attached to it, whereas the charger should be outputting 22-24V.

The green light on the charger stays on, but only the ‘low battery’ red light on the roomba remains on while connected to the charger.

It’s a roomba 690.