[Nut-upsuser] Where are usbhid-ups driver parameters defined - and what do some of them mean?

[Richard Chapman]

I am using the usbhid-ups driver with a Belkin UPS.
upsc shows several parameters which I would like to both understand and 
probably change. In particular the following part of upsc output:

battery.charge.low: 30
battery.charge.warning: 30
battery.runtime: 120

My questions are:

1) What is the difference between battery.charge.low and 
battery.charge.warning? I presume these are % thresholdsWhich of these 
triggers the low battery event?
2) Is there some way to change these? 30% charge seems to me to be 
sailing a little close to the wind. As the battery ages - I'm sure the 
UPS will cut out long before "zero" is reached. Also - if it comes back 
up with  < 30% charge - and another power fail occurs soon after - that 
is not good. Are these set i the source code - or is there another 
config file somewhere. upsrw doesn't appear to be able to change these.
3) What exactly is battery.runtime.

Can anyone point me to documentation which describes these parameters?

Thanks

Richard.