Back-UPS HS 500 runtime calculation

[r__k_apc]

Understood that the Back-UPS HS 500 is EOL at this point.

I have an 120V US HS 500/BH500NET that is functioning properly, other than the displayed runtime on the web page. Replaced the battery recently. Battery and HS 500 pass self-tests.

At a 20-25W load the unit runs for 90-100 mins on battery, which is great. Again this is what I actually get, not (just) what a spec sheet or math says I should. That's not the problem.

However when fully charged, the unit's web page displays only 45-50 minutes of runtime when fully charged, no matter what I do to recalibrate it. I have done:

- the 30% load discharge calibration numerous times

- various variations of that discharge calibration

- resets from the web page, the management software utility, and the little pinhole

- putting in other batteries including older ones

and I can't get/don't know how to get the web page to reflect the real runtime.

I get the fact that at that point on the curve, the math may be fuzzy (runtime chart): http://www.apc.com/products/runtimegraph/runtime_graph.cfm?base_sku=BH500NET&chartSize=large

I also found this old thread which describes a related (sort of the reverse) problem, where the person believes he should get 1:33 of runtime (which is what I actually get) but does not, albeit at 230V.

http://forums.apc.com/spaces/4/back-ups-surge-protectors/forums/general/1542/brand-new-back-ups-hs-5...

My question is - is there any other undocumented way to reset the runtime calculation or battery constant to at least get the displayed runtime closer to the actual runtime? There are human procedures that are impacted by the displayed runtime calculation, even if they are to my favor due to the difference - so it's somewhere between a major problem and a cosmetic one.

I see reference in other websites to a procedure using a serial connection to set up a terminal session to the unit's serial port and reset the battery constant - is that a possible thing for the BHNET500, even if it is unsupported? I don't have the proper RJxx-to-USB cable and don't want to make or buy one if that's not even possible.

Thanks