Basically a 12V sealed lead acid battery 7 Mah. Any opinions on how they would go? I'm a bit worried about constant voltage output - and would need to get the polarity right!
I have been using similar rated 12V 7AH batteries exclusively with my ETX-125. I have two of them built into a power box with the battery charger / mains power supply. The power supply supervises the battery and indicates a low bettery condition which allows me to switch to the second battery. The power supply also will cut off the battery before it is deeply discharged, if I ignore the low battery indicator. Deeply discharging these batteries will significantly shorten the life span or destroy the battery entirely. That being said, a fully charged 12V 7AH normally will run my ETX-125 for a four hour plus viewing session as long as I am not doing a tour with excessive slews. I will run accessories such as dew heaters off of the second battery. Having it all (batteries, power supply, dew heater controller, accessories power outlets with power conditioning) built into a tool box allows for easy transportability and if viewing from home, allows me to run on mains power while charging the batteries.
Enfield & Tjmck to I.I.S.
The 12V 7ah battery is good for what you want.
Check around for a better price.
Jaycar and Dick Smith have these batteries for $29AUD.
If you are going to drain a lot of power from the battery, go for the deep cycle version instead, they look the same but are approx 40% dearer to purchase.
I found that 7Ah was only just adequate and had to be freshly fully charged at that to work well. Really need 17 Ah. Obviously, more power gives opportunity to add other bits and pieces and a large battery can be hooked up to octopus straps to give extreme stability to the rig . I have a big heavy 75 Ah battery which may be overkill, but I can be confident that I have enough juice to handle any bits and pieces I want. With the occy straps attached to the rig, Willie Mason would have a hard time knocking over my setup . You must be careful to not reverse polarity or you will blow your board and have an expensive repair - I know, i have done it .
Last edited by space oddity; 19-10-2008 at 06:46 PM.
Reason: forgot to put in important point
I work in the Fire Alarm industry here in Canada. Most Fire Alarms in Canada, not sure about Austrailia, work on 24V derived from 2x 12V gel cells. They are normally anywhere from 4.5 AH up to 135 AH batteries. These are tested annually and normally replaced well in advance of the depletion of the life span. The Fire Alarm companies usually pay to have the batteries re-cycled. If approached, I am sure they would be willing to flag the better ones and give them to you rather than incure the expense. I like the 12V 7AH batteries for the minimal weight. As my post said, there are two in my power box - a primary and a back-up or accessory battery. I do like having a back-up battery vs. putting my eggs all in one basket. My box will allow for the substitution of 12v 12AH if required - have never found the need with the exception of once where it was very cold and I had the dew heater on to keep frost off of the optics.
I have a ride on golf buggy that uses 4 12 20Ah deep cycle batteries. They only give full output for about 100 re-charges and then I need to replace them (or walk home). The old batteries however make great power supplies for my LX200 and ETX125 telescopes that last at least all night and I also have two of them paralleled up that I use in my walking type golf buggy that give better service than the standard type.
I use a standard modern 12 volt automatic charger ($17.00 or something at big W) and run the charger through a timer set for 6 hrs (avoids over charging). The old batteries have been in use at a second life now for 6 months without bother and I have two left for any one who would like to pick them up.
Readily available in Australia, normally from ex-cellular phone sites etc. In Brisbane, AAA batteries at Albion used to (2005) have all sorts at really good prices, mainly larger sizes. I used them for years on my boat.
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