Hey Gary, was great to finally meet you, felt like I had known you for ages
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Something else I would take into consideration is if you intend taking your mount into the field, ie, star parties etc. The G-11/Gemini draws a considerable amount of power during slews, about 3 amps from memory, so any battery power has to be able to supply that sort of power, another thing is that the Gemini does not like straight 12 volts, it likes a regulated power of around 13.8 volts to operate without motor stalls.
It is my intention to equip my GM-8, which is my field mount, with an AN in the near future because of the power requirements.
Cheers