Geoff,
The chargeing booklet is from pre 1982 but the main difference is you will not need to cycle or exersise the battery like helped the old nicads.If you use the ET flasher often times a week then you may need to fully charge(18 hrs 10-12 inches to 75-100 watt bulb) once a month.But over charging to a significant level is not likely.No sense keeping it in that 10-12 inch distance longer than 18 hours though.Also window sills are not as good as one would think.It heats everything up to 110 Deg F and above. Plus remember the window itself robs some of the suns effective light traveling through for charging purposes.Heavy paper clip on the side of an old large shade still works well if folks still have one.I even use a small fan near the bulb to keep them charging at a lower temperature but that is not necessary if you charge further than 8 inches to a 75 watt bulb.