Several Tripp Lite UPS units will not start up

Hi, I have 3 USP devices: 

Tripp Lite SU1500rtx2u x2

Tripp Lite SU2200RTXL2Ua

They have been in storage for a few years, and this weekend I went to fire them up for a client, and none of them will start, cold-start, or anything at all.

I placed a known-good test battery into each.

They all have AC supplied.

No pass-thru power.

The breaker is not tripped, and I see continuity between the screw terminals.

Internal fuses are all good.

I see 12 volts to the Aux battery pack connector.

What else can I try..?

Thanks!