Telescope Reviews: What size generator is needed?

The issue you haven't addressed is how much power you'll consume for each night's observing. You have 62*12 or just under 650W of power available. Assume that it's warm (no cold effects to decrease battery performance), and that you can actually use 80% of the battery's rated capacity. This gives you 470W of power available.

If you're visually observing, the only thing you need to power is the mount. Assume an average current draw of 1.5A/hour, round up and you'll need 20W/hour. Your existing battery should last for 470/20 or 23.5 hours. You'll only have 6 hours observing time a night at this time of year so a single charge on the batteries should last for almost four night's use

If you're imaging, the power equation changes drastically. The most common mistake made is to get a small 110V cigarette lighter inverter to power the computer. This means converting 12V dc to 110V ac then back to 18-20V dc to run the computer. Two voltage conversions, each with its own power losses is the quickest way to drain a battery. A better approach is to get a 12V power supply for the computer. A single voltage conversion will cut conversion losses by 50%. Examine your laptop's battery with a magnifying glass. The battery's capacity will be part of the information printed on the label. An 85W battery that (supposedly) runs the laptop for four hours means that the average power use is just over 20W/hour. All equipment running on voltages between 5V and 12V should be powered from DC-DC switching regulators. One of these nifty devices will give you 2.5A at 5V while drawing less than 15W from your 12V battery. Two USB powered imaging cameras and a hub will require less than 10W/hour from the battery.

If you're running a full imaging setup, with computer, you could need the following power from the battery every hour:
18W mount
07W guide camera
25W imaging camera with cooling
25W computer

This totals 75W/hour which means that the battery should last for 470/75 or just over 6 hours. Gel cell batteries are usually rated when used at the 10 hour rate, which you've exceeded. Capacity, in this case, should be downrated somewhat, so you'll probably get around 5.5 hours of battery life. Dew heaters, while easy to run off of 110AC power in an observatory, usually require large (heavy) deep cycle lead acid batteries for field use.

To recharge the batteries, you need to figure on inputting 120% of the power drawn from them. If you use 500W of power at night, you'll need 600W of power to recharge the battery. If you figure on 12 hours a day of sunlight, you'll need 50W of power/hour from solar panels for the imaging setup but only 10W for visual observing. Solar recharging can be handled for a visual observer using readily available solar chargers from Harbor Freight Tools. Don't forget that a solar panel only generates its rated output when directly facing the sun. A fixed panel's average output will be less than its rated output.

Another possibility for recharging your batteries is to use the charger you'll be bringing with you, your transportation. A set of jumper cables and an hour or two connected to your vehicle should easily recharge your battery. Even at 2 gallons/hour, a very high gas usage rate at idle, a two hour charge run will cost less than $15 (this week). Compare this cost to $320 for a generator and a couple of 5 gallon gas cans and it may be a cost effective option.

Phil