Two wires not much weight,yes a we gel
battery would be ok.
Or maybe not. I tried that with my 15 hp Yamaha and it didn't go well. I only need the
battery for starting duty, operating the power trim, and a minimal amount of electronics, so lugging around the 70Ah wet
battery originally installed seemed silly. I thought I knew better and put in an AGM motorbike
battery instead. Well I was wrong. It only lasted a couple of long runs before it had electrolysed all the acid, thankfully it vented rather than exploded with the pressure.
The charging output of small outboards is typically just a coil excited by the magnets on the flywheel that also excite the ignition. Either output as rather rough AC to power e.g a masthead light, or put through a bridge rectifier to deliver some very choppy looking "DC" to charge a
battery. All varying with engine revs. They are what they are. Anything better would just add complexity and cost.
That motorbike "regulator" might work, AFAIK they just clamp the voltage to a sensible level and burn the excess power off as heat, which offends my engineers instincts. But then they need airflow, see the cooling fins ? You can't put them in a sealed box. That's not going to work on a boat in a marine environment, dinghy or something bigger like mine. If it lasted a season before corroding to bits I'd be surprised. Maybe you could find space to put it inside the engine cowling, protect it but no airflow there either except for the engine air intake, actually more likely to cook it. Anyway I couldn't it's absolutely packed with beautifully engineered components.
The 5 hp yamaha for the rubber boat also has the same "lighting coil" output and the same connector, but I've never used it. I expect it would be less pokey than that of the 15 hp on the mother ship, maybe a small motorbike
battery could cope with that, I don't know and don't have a need.
I could make a very good efficient regulator myself, I have the knowledge and skills and know exactly how to do it, but I'd rather just buy one if they exist. Otherwise there might be a small business opportunity to exploit, if there was any demand. But they would not be inexpensive, for a properly marinised product, with distribution, advertising, backup and warranty, even if people recognised that they were a good thing and bought them.
Meanwhile the big heavy wet
battery is back in, bottle of distilled water to regularly top it up, it'll do.
Sorry if none of that was any help. I'd just say, take a charged up
battery, suitably sized for whatever gadgets you want to connect, when you go out in your dinghy, and charge it up again when you get back home. Connecting it to the motor is a nice idea but it is a very crude arrangement on small outboards.