It's supposed to charge itself.
But!!! if the battery goes dead over time, the radio or depth finder might be killing it.
You can install a volt meter in the system.
Get a battery load tester(Harbor Freight $25) and a hygrometer.
That's 2 of the handiest tools I use.
There are many options for battery testers, chargers.
I have a big shop charger with a 200 amp jump,30 amp quick charge and 2amp trickle charge.
I also have a battery maintainer that sets on a shelf( don't trust it??? )
One easy test is using a simple test light.
It tells you if there is any draw on the system.
Turn everything in the boat off.
Unhook the ground lead on the battery.
Install the tester between the N post and the end of the cable.
If the tester lights up??? then there is something drawing on the battery.
Then go through and pull the fuses or unhook the accessories and see what circuit stops the light from burning.
