I have my little battery for my electronics. It is about the size of a brick. It has a trickle charger I ise for it overnight after I use the battery. Question is, can I use the trickle charger for the big "car" battery that is used to starty boat motor? If so, do I have to take it out or can I connect it while the terminals are still attached while the battery is still in the boat compartment?

Well, we ran out of juice in the cranking battery last weekend....very interesting few hours. At that time, our electronics were run off that battery, we've since added it's own dedicated battery. We have ours wired in with the trolling motor batteries with a permanent wire running to the negative, and an alligator clip for the positive. Same from the trolling batteries to the cranking. When we get home and plug in the 3 bank, we clip the alligator clips and it charges out electronics battery. Kinda a frustrating way to wire everything together, but it works extremely well. Hope this is easily understood. I'll draw out a diagram if needed.

So in my case I could just still connect the charger directly to the battery while it is wired with the terminals?

I'm not certain considering I'm not the most technically minded person. If a trickle charger works on the same premise as a 3 bank, then yes. Then all you have to do is open your storage and plug in the charger.

Yes, you can attach your charger to the "car" battery without removing other wiring.  You can also attach all other electrical equipment to the "car" battery.  Your trickle charger will work to recharge the "car" battery, but it will probably take several hours, or even overnight to do so.

The amperage to charge larger batteries is higher. If there is any draw while charging it will take even longer. The correct size charger is the best answer

I agree.  You will want at least a 10 amp charger.  If you have other equipment attached to the battery, make sure they are turn off.

Works well!!! 8 hours until green light charge. Thanks guys!!!!!