Always a good idea to prep for a star party… in advance!
Case in point, Fall’N’Stars 2010

Last year, you may remember, we took the Centre’s portable power pack (the big one on wheels) to use on the Douglas telescope and it failed miserably dew wise. We opened it up to discover that 3 of the cells inside had ruptured and had leaked and basically we wrote off the 7 year old unit.

This year, the last item that I packed was a car-sized deep
cycle/rechargable Nautilus battery.

We hook up the dew gear on our 20cm dob and none of the lights on the controller come on. Hmm. another bad controller? (We had out Kendrick controller die a couple of years back).
After a lot of wiggling wires, we gave up on the battery and hooked into the vehicle power. That worked! lights, power and heat on the eyepiece.

Back home I took that large battery. hmm read only 3 volts DC. Hook it up to the trickle charger. Nothing… the charger says there is nothing there.
Hook it up to the regular large battery charger. hmmm no current
So I opened up the battery lids.. Hmmm. looks pretty dry. 4 litres of
distilled water later the charger started working.
Yay! It starts to bubble as hydrogen gas is produced as a charging
A few hours later I find a large puddle of water on the battery, in the
box and leaked out onto the table…
hmmm not water.. sulphuric acid!
A box of baking soda later, the acid is neutralized and the battery
rinsed off and taking a break until I find a better charging location.
But the battery is now reading over 12vdc!

The moral of the story… better prep work (and battery maintenance!)
will make your observing session a better experience.