HP105B Frequency Standard- Fixer upper

This is a Hewlett Packard HP-105B High Stability Quartz Frequency Standard. This generates simultaneous outputs of 1 mhz, 5 mhz, and 100 khz, through BNC connectors on both the front and the back.  The individual meter pictures show the outputs on each frequency setting, so you can see all three outputs work.  The frequency counter (not included) shows the actual 5 and 1 mhz output. It appears to work fine, though there seems to be a problem in the power supply department.  After it has been running for a while, a real mechanical buzzing starts to come out of it, like there was a bumblebee trapped inside.  It appears to be coming from a relay that I believe switches it between battery backup and ac source.  Since this appears to have the original battery, I suspect the battery is bad, and the charging current is pulling the power supply voltage low, causing it to want to switch to battery.  The battery voltage I suspect is low, causing it to switch back to AC, making it cycle back and forth rapidly - buzzing. When you switch the battery charging switch from full charge to trickle, the frequency outputs drop to zero.  I personally suspect the battery, but as my late father was the expert on these things, and I don't have a manual, I can't be sure. Comes with the AC power cord, but no manual though.

Winner to pay actual shipping costs (22 lbs from zip 20197).  Money order, US currency, Check (must clear first)), or Paypal accepted.  Thanks very much for looking!