We a small super cheap panel we got maybe 15/20yrs ago for camping
A jumper battery unit runs 12vautomotive florencent trouble lights in the tent rooms... walking in turn on the switch on the pole
The panel plugged in and thrown on the tent roof ...
I now have velcro stuck to the top of the outboard and bottom of the panel
The battery box has a cig lighter unit mounted in the lid,,with rubber covers on the holes...
and fused inside the lid.. with a good length wire...direct to battery, by passes the main power switch.
So come home.. drop the solar unit on the velcro on top of the outboard, plug into the battery and it is enough to maintain full battery charge over natural leakage etc.
The top of the outboard is because of location close to battery but still out of the way ... and the sun catches this part of the boat as it is stored under a huge sail /carport area.
Due to the number of panels in the small unit it cant over charge the battery, ie when charged the out put of the panel equals the output of the battery (bit simplified but u get the idea?) and when sun goes out the diode inside preventives any discharge
A huge secret to long term lead battery life is maintaining full charge and full storage.
If have duel batteries and both just running sterio.and voltage drops down to 11.5 get them checked.....
With a little automotive jumper unit (which we use as spare jumper emergency battery also) running the floro cabin lights, sterio, sounder/gps , floro lights on the deck for night fishing...and not firing the engine up and dark.. solar panel not hooked up... from a full charged battery beginning of the evening to next morning it drops to just under 12V
This has far smaller storage than a normal, let alone heavier duty boat battery... let alone duel batteries...
Next morning .. after a coffee turn on the main battery switch... pull the cig lighter from the jumper battery (which goes to the boat dash cig lighter) fire the engine, pull the anchor, then plug the jumper battery back in to be recharged off the outboard.
Also one should be for running aux stuff.. stereo , sounders, off one battery, and the other battery for motor starter...not both run both....
And like with the jumper battery, fire the engine on the engine battery, give 5 mins or so... then switch both batteries on for charging
In a thread a while back, it is apparent that outboards only have small capacity alternators, 20/ 25 amps or something.....the chev has 105 amps and stock had 64 amp as a comparison
Let the engine battery recover , then connect the over night battery (both together is fine as they should be wired in parrell.