Originally Posted by jab
I didn't set the thresholds with any particular energy capacity in mind. Instead, I set the "critical" threshold at 10.5V, since I read at
http://batteryfaq.org/ that discharging a lead-acid battery below that level is a no-no. Then, I just looked at a voltage-vs-time plot of my light system discharging, and eyeballed the battery voltage that corresponds to "about half an hour until 10.5V" with typical use. This came out near 11.5V, so that's where I set the "low battery" warning threshold.
Well the *low battery* warning would have been great on tonight's rainy return commute. On a fresh battery, I can usually make the round trip. But there were some errands to run also, so I found myself "rationing" in well lit areas so there'd be enough juice for the dark ascents.