A solar panel 15 W with a controller

sadly, 15W is not a lot of power, when used alone. i don't remember what the loaded voltage of those panels are. perhaps 13v, which means they support a load of around 1.15A. bear in mind, that is with very clean panels, and in direct burning sunlight.
I had a similar panel and charger kit, and it averaged about 0.7A in direct sunlight.
for a battery, i would suggest something in a small sealed maintenance-free battery. one similar to this: Tenergy 12V 7AH TB1270 Maintenance free Sealed Lead Acid Battery SLA Battery 844949006392 | eBay
it is small enough that your solar panel would have the capacity to charge it.
not sure how much electrical skill you have, as far as wiring stuff up, but i would then add a 12V socket to plug in a cell phone car charger, for charging your phone.
as far as lighting a light, i would stick with low power consumption LED lights.
do not use an inverter with this setup. not sure what kind of camping you do, but this setup will take a while to charge. but a 7AH battery, like i linked to (you don't have to get that one, it was a example), will charge a phone several times on one charge. but an inverter will use a lot of battery power, fast.
and as far as using a car battery, it will take your camping trip duration to charge it.

it is still a fair solar panel, and charge controller, don't get me wrong. but there is a common misconception that because the charge controller says 7A, that it will charge at 7A, regardless as to the size solar panel. in reality, it would take several solar panels to get 7A of charging output.

my camper has a single 100W solar panel that i use, so far, to just keep the large deep-cycle marine battery up to charge when i am not using the camper. if i apply much of a load on the battery, the 100W panel will not keep up, because the battery size and load are too much for my current setup to handle.

but like i said above, your setup will be fine to charge a small battery, and use that small battery to charge a cell phone through a car charger.

Hope this is helpful for you! and welcome to the forum!

Thank you for your useful points. While I am trying to remember all I learned about this stuff in high school, this could be a great experience for me as a beginner in the area of solar panels. In general, my plan is to use it while camping just to charge cellphones and maybe a laptop. So, the only concern that remained is the mobile network coverage! 😃

I love the idea of small batteries plus the 12V socket with a few USB ports. I saw some like this that are around 150 W. Would that be too much for a small battery?

Also, is there any way to use a power bank instead of a car battery that going to be charged by the panel? Something like this: Solar panel>> controller>> 12 volt socket >> ... >> power bank >> cellphone. Although I know it is designed to be used with a car battery.

Thanks

Having been in your shoes;
I would suggest that you first determine what you want to run and how long you want to run it.

Some basics;
Usable energy from a battery can be commonly figured in Amp Hours (amps x time in hours).
A milliampere is 1/1000 of an amp, thus 100 ma (milliamps or milliaperes) is 0.1 amp.
Lead acid batteries should probably not be discharged much below 50% for best longevity.. so if you have an 8 amp hour battery you should probably only depend on it for 4 amp hours worth of electricity... if you run it flat it can damage or destroy it.
Small solar panels can be viewed as trickle chargers.
Inverters draw current except when they are switched off, how much varies from inverter to inverter. a very efficient small inverter can draw on the order of 100 ma at idle (no load) a less efficient small inverter can draw 1/4 of an amp (250 ma).
How satisfied people are with a solar electric camping setups usually seems to depend on their having realistic expectations and their ability to limit their electrical consumption to realistic (depending on their set up) levels,
I have used batteries for camping for quite some time (decades).
I even tried those little 7-8 AH batteries (very much on the small side)
Used automotive starting batteries can be utilized but because they are designed for high current ove sort time intevasl the usually don't work all that well (and when stored for unknown periods of time their plates regularly have sulfation problems resulting in reduced capacity (figure about 30 AH for a good automotive starting battery).

Near the end of my backpacking (knees are giving up) I tried a rechargeable USB power pack and it seemed to work relatively well with a modified LED USB headlamp. The problem, at that time, was that the panel weight was excessive for backpacking IMO... much lighter and higher powered USB compatible panels are availiable today; however they will likely still require a tangle of cords.

Here is a pic of a quite old small solar setup that I used semi-successfully for many years;

it consisted of four 8 amp hour sealed lead acid batteries(in parallel) = 32 AH with an approximate actual capacity of 16 amp hours. Mostly I charged it at home using a trickle charger and took it weekend camping to power a relatively inefficient 120 volt compact fluorescent bulb (in the pre LED stone ages)... It worked to supply me enough light in the tent to get ready for bed for 3 to four nights. The 5 watt solar panel was never really effective at recharging the battery. The Coleman inverter was, much too large for the battery bank, it was a power hog and was eventually destroyed by a near miss lightning strike.

A better more recent system;

Two 7 watt (unrealistically rated) panels and a 35 amp hour sealed lead acid deep discharge battery powering a (now obsolete) Harbor Freight 80 watt inverter.
This system can/could recharge the battery in approximately 1 1/2 rimes the length of time that it is/was used to power a 120 volt 350 lumen LED bulb, drawing a bit over 0.6 amps at from the battery (including the inverter).
Note; small panel chinese manufacturers often vastly over rate their panel outputs. These obsolete panels can provide; when properly angled in direct clear sky sunlight as much as 0.3 amp at 13.8 volts each (varies depending on the state of charge of the battery).
Note; these panels were used as a trickle charger directly connected to the battery without a charge controller but the battery was closely monitored via a digital volt meter (baby sitting batteries is boring) to prevent over charging and boiling the battery (not terribly likely with such low currents but possible.

This provided tent lighting and powered tunes in the tent for about the last 5 years and the battery only recently died.
It was charged at home initially and the solar was only used to provide some charging on Trips longer than about 4-6 days..


The battery has been replaced by a 50 amp hour Lithium Iron Phosphate (LiFePo4) battery. (which supposedly can be run close to flat with little to no damage)

...sorry if I ramble a bit but I'm getting increasingly antique...

Enjoy!