kohjb wrote:Yup. I too do have the Celestron Power Tank, but I have the NiMHs as backups which are left in the ETX. I know the voltage is not the same spec wise, but the characteristics of alkaline batteries are such that their internal resistance is pretty high, meaning that their voltage drops pretty fast as it gets used. Take a look at this page from Weasner's site. The pertinent info is not so much about the low temp but rather how the voltage drops. The good thing with NiMHs is that their internal resistance is low, so their voltage stays pretty constant, but the problem because of this is that they die suddenly, so you won't get much warning.
http://www.weasner.com/etx/techtips/200 ... temps.html
I got these Sharp 2500mAh ones, and the Sony fast charger. With 2500mAh, and an average consumption of 200mA, one charge should last about 12 hours. I'll have to admit that I haven't used em much since the skies have been so cloudy. I may have to eat my words :oops:
A big plus for me though, is that NiMHs don't LEAK !! I don't know about you guys, but I absolutely hate it when my $XXXX equipment is ruined by those stupid leaky alkalines !!! :violent: I sometimes get a panic attack when I remember that I haven't used my scope for a while and I had left the alkalines in them !! :k-crazy:
Personally, I think the Celestron power bank is an overkill unless you are connecting it to a few goto scopes or you want some sort of heater supply. My 4AH gel battery can last more than a whole night and small and compact. I fully charge it, leave it in the store room for 2-3 months and after taking it out and charging them, it goes back to full charge within 5 min!
NiMH are ok as they dispense with the need for an external battery but problem is I use an adapter plate to connect to my manfrotto tripod and hate to always unscrew the plate each time I need to charge the batteries.
the gel batteries work beautifully. Since I have no batteries in my ETX, I don't worry about leakages. Incidently, if that is a problem, can always put in Eveready Lithium battries, they don't leak...
and yes....my scope has not been seeing much action due to poort weather. in fact, I only powered it twice since I came back from the last mersing trip (was it in July?). Once to oil the gears and run it a few rounds to keep it shipshape as well as update on the autostar software and another time to do some observation my my home multi-storey car park..
i guess alot of people have been disappointed they were unable to join WWF-TO ( Weixing's World Famous Tampines Obseravtion ) due to poor weather this past few weeks.
rich
"The universe is composed mainly of hydrogen and ignorance." 
