Appropriate battery for overnight viewing to drive telescope and GOTO?
Before buying anything, get out your Amp-meter and measure what the motors pull in clock drive and GOTO mode, starting from a variety of scope positions.
An 18 incher will have a lot of mass, and Dobsonians are not known for their excellent bearings, so the amount of juice you need for a night of observing could be considerable.
Do you track most of the time, or GOTO...GOTO...GOTO?
How many hours is your typical observing session.
Multiply your average tracking amperage by the approximate number of hours you spend tracking, then do the same for your GOTO work.
Add the two numbers (amp hours) together, and double the result.
That should tell you about how big a battery you need.



The doubling is done to provide leeway, and because taking a standard lead acid below 50% is a sure way to kill it after only a few recharges. If you go Li, you can probably cut the multiplier.