Electrical Engrs. -------> UPS Battery help needed


I am using a UPS for last one year and it has 2 batteries attached to it.

During the last 11 months the run up time was around 1- 1.5 hours, it has suddenly drop to 40 mins in this months, meaning I need new batteries.

My question is is there a possibility I can attach 2 new batter along with these batteries to have better and longer backup.

Will is effect the charging performance of UPS or batteries.

Or its best to attach only 2 batteries and dispose of these older ones.

Guide me and Thanks in advance.

The charger in your UPS is designed to charge 2 batteries. If you attach 4, it will:

a) either overload the charger hence never fully charging the batteries

B) if not overloaded, it will take longer (roughly double) time to fully charge batteries

The proper way of using more batteries is to do the following:

1) Install separate chargers for additional batteries (1 charger for 1 large capacity battery. If you batteries are less than 50Ah then you can use one charger for two. You need to check with the salesman about how much capacity the charger can handle). Under normal condition (Electricity available), the additional batteries must remain disconnected from UPS

2) When lights go out, connect the additional batteries to the UPS to enjoy additional backup time. Be careful of +ve/-ve terminals. As you have two battery setup, additional two batteries will connect in parallel to your existing two batteries. Parallel meaning +ve to +ve and -ve to -ve terminals

You can use a switching mechanism (can be auto or manual) to connect/disconnect additional batteries to UPS. In case of auto switching, some kind of relay is needed to sense the presence of electricity and engage/disengage batteries to UPS.