|
John,
Fair enough comment. The DC (deep-cycle) batts. as you say are certainly a better unit.
I don't know where Ian is located. It may be that he sits out in the 0 to 5C nights on top of some mountain or in the Alice in mid-winter and yes, under these conditions the old lead-acid gives a poorer performance, but I don't think a DC goes any better than a standard under these conditions, as the performance is chemistry related rather than dependent upon the thickness or otherwise of the plates.
If other equipment is to be used, there are heavier duty "jump-starts" available, eg 25 AHr. A dew-heater will use at the most 1A (unless its a very large scope - my 6" uses only about 0.6A). What else is there? A lap-top? Maybe, although these tend to have a battery with a reasonable operation time.
I think the real answer lies in the correct useage and maintenance of the battery. Not discharging it beyond 50 - 75% capacity nor allowing it to stay discharged for an extended time. For a 25AHr battery therefore, the maximum discharge should be say 15AHr. At the max. discharge rate of 10%, (ie 2.5A continuous) this represents 6 hours of operation. Should be plenty.
Then recharge the next day. The intelligent charger built into the "jump-start" or power-tank, should handle this comfortably within the time available before the next night's viewing.
Robert
|