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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.
tjmck
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