You may get a real small spark when hooking up a battery but if you are getting a bigger spark you may have the battery hooked up backwards... Find the word "NEG" or the symbol "-" printed on the battery case and make sure the cable that is going to this terminal comes directly from FRAME GROUND very near the battery. It is real easy to to get these cables reversed...
The automotive ceiling lamps and the heater fan motor are very big 12VDC battery drains. You can change the ceiling lamps to LED lamps and save as much as 80% load for each lamp. Not much you can do with the 12VDC heater fan motor. It draws around 6-8AMPS when running.
Just a thought
Roy Ken
My Posts are IMHO based on my experiences - Words in CAPS does not mean I am shouting
Roy - Carolyn
RETIRED DOAF/DON/DOD/CONTR RADIO TECH (42yrs)
K9PHT (Since 1957) 146.52M
2010 F150, 5.4,3:73 Gears,SCab
2008 Starcraft 14RT EU2000i GEN
2005 Flagstaff 8528RESS