I have a 2-3 year old 7Ah 12V Ultracell. It has been in a UPS for 2 years.
No matter how much I leave it to charge, after disconnecting the charger, the voltage quickly dropps to ~13V (in a couple of minutes).
What is wrong with it? How can I fix it?
The battery holds a charge and can output >2A without problems. I run a soldering iron (20w) from it, usually for more than 40 min.
I have added a bit of distilled water, but no difference in voltage.
I let it charge at 14.5V, max 1A and after ~6hours the pressure increased and I released it. (Voltage was at 14V)