OPTI UPS Model ES-1500c
Battery RBAT9 Replacement Instructions

OPTI-UPS Enhanced Series ES1500C

Remove power plug and relocate the OPTI-UPS Enhanced Series ES1500C power unit to a suitable workspace.

Back side of OPTI-UPS Enhanced Series ES1500C showing available power connections.

Remove 4 screws from back side of the UPS.

Remove 2 screws from sides of the UPS (1 per side)

Remove 4 screws from bottom of the UPS.

Slide cover off by slowly pulling backwards.

Side view of power supply with cover removed showing battery location.

Remove front panel by gently pulling forward. Start by pulling at the top. Do not pull too far as it remains connected to the power unit by a short electrical cable.

After removal of the front panel cover, place cover on top of unit to get it out of the way of the batter cover plate. You may also opt to disconnect and remove it completely.

Remove 3 screws from battery cover.
Battery cover will swing outward.
Remove battery cover by pulling outward from hing slots.

The old batteries slide out the front, but may stick to the plastic bottom container. You may have to forcefully pry out the old batteries and "un-stick" them any way you can.

 I had to cut the front of the plastic container to allow removal of the old batteries.

Replacement Batteries are delivered as two separate batteries. Remove the cardboard connection protection and discard.

Tape the two new batteries together on the top and bottom sides in a similar fashion as the old batteries are taped.

Old batteries removed.
New batteries taped together and wires connected and ready to be installed into the power supply.

 Batteries (RBAT9) Replacement Instructions as scanned from the OPTI UPS Model ES-1500c Manual.

I found these instructions useful as a guide but they had some errors in them.