Good Neighbor Wilson, its just as easy to install a 235 watt panel as it is a 100 watt, so I suggest you go down to the south Odon Amish community and buy a 235 Watt panel like I did (I bought two for my RV, they measure 39 x 64) from Wagler Energy Solutions for $211.50 (90 cents per watt) and install at least one of them.
To properly charge your battery you need a Solar Charge Controller (interface from solar panel to battery) which aren't expensive for say a 20 amp cheap PWM type, but I wanted a Smart 3 Stage (Bulk, Absorption, Float) temperature compensated MPPT controller which cost more, but you can get by without. In fact some of the smaller panels come equipped with their own PWM controller mounted right on back the panels, simply plug and play to your 12 volt battery. Two wires piece of cake.
For RV or home energy use I suggest a couple true deep cycle 6 volt golf cart batteries (like Trojan T-105 or equal Sams Club or Interstate etc) wired in series, they have thicker plates and are better at deep discharge and recharge, however sure a cheap regular 12 volt auto/truck starting battery will "work".
If you need any 120 VAC powered by your battery you would need an adequate sized 12 VDC to 120 VAC Inverter. Modified Sine Wave MSW are cheaper, but if you have sensitive electronics and some appliances prefer a more expensive Pure Sine Wave PSW Inverter. Sure a cheaper MSW Inverter will "work" fine on many devices
NOTE if you're going to do this and need to store a reasonable amount of energy, a regular auto/truck starting battery may only have say 100 Amp Hour energy storage capacity while those true deep cycle 6 volt golf cart batteries like my Trojan T-105 have a 225 Amp Hour rating. Those so called 12 volt cheap RV/Marine batteries sold at Walmart are semi deep cycle at best and will work but don't store the energy a quality and proper sized true deep cycle golf cart battery does.
My advice, buy a 235 Watt Solar Panel ($211.50) fixed mounted pointed to southern sky at around a 47 degree tilt angle,,,,,,,,,, a 20 amp PWM Solar Charge Controller (unless you buy a panel with built in controller),,,,,,,,,,,,a couple true deep cycle 6 volt golf cart batteries,,,,,,,,,,If 120 VAC is needed a 12 VDC to 120 VAC Inverter adequate sized.
Sure your 100 watt panel proposal (need a solar charge controller) and any old cheap 12 volt auto/truck starting battery will work subject to your needs.
John T Retired Electrical Engineer
2006 Gulf Stream 29 Ft Class C Ford E 450 Super Duty w/5 speed 5R 110 OD Tranny
470 watts of Solar Panels, four Trojan T-105's in series parallel for 450 Amp Hours
30 Amp Smart 3 stage temperature compensated MPPT solar charge controller
80 amp Smart 4 stage Battery Charger, Progressive Dynamics 9280
4 KW Genset
86 gallons fresh water, 66 gal gray water storage.