how do these things work? i found this one on Academy:

http://www.academy.com/webapp/wcs/stores/servlet/Product_10151_10051_135403_-1?Ntt=on+board+battery+charger&Ntk=All

but i dont understand how it works.... my boat currently has no charger, so what we do is use two batteries, one hooked to the starting and trolling motor, and the other one as spare... with this setup we can fish all day, starting the engine and trolling.... by the end of the day, the battery wont have enough power to start the engine, so we just hook the starter to the spare (smaller) battery, and keep trolling with the big battery.... we have never had a problem with this, however, i would like to have an onboard charger...

You should just keep the smaller battery hooked to the gas engine to start it and use the big battery hooked to the trolling motor. The on board charger is used for easily charging your batteries when you get back from a trip. The on board charger has wires that you wire to your battery so when you need to charge them you would usually just have to plug the male end of the battery charger into the female end of an extension cord.

They are really nice to have, especially when you have 3+ batteries on your boat you wish to keep charged. Just plug it in and leave it plugged up. Boat is always ready to go!

Jeff

The charger works when the boat is in the driveway, plugged into a wall outlet. It wouldn't solve your issue with switching batteries now. For starting, you want a marine cranking battery. For the trolling motor, a deep cycle marine battery is what you want. They are different. My guess is the smaller one is a cranker, and the bigger one is the deep cycle. As was mentioned, just hook the engine up to the cranker, and the troller to the deep cycle.

thanx for the info!!

so, this is not going to solve my problem... i was told my motor had a charging system but it doesnt works, i will see if we can get it fixed...

and, the reason why i use the big battery for both things until it can no longer start the engine, is because this way, i will have the smaller battery charged for when i need to start... i dont want to risk it having the big one for trolling and the smaller one for starting, and then, by any reason, drain both of them enough that i can keep trolling but i cant start the engine.... this way i know that even if i completely drain the first one, the other one will have a full charge and be able to start the engine without a problem....

btw the big battery has 2 sets of poles, 2+ and 2-, supposedly it is for double duty... maybe later i will get deep cycle batteries, Optima would be nice, but for now, i will have to do with what i have... the smaller battery is one we got for the ATV which we never use, so we removed the battery and put it in the boat as spare.... and it has saved us from rowing, a lot of times....

i was told my motor had a charging system but it doesnt works, i will see if we can get it fixed...

Probably looking to replace a bad rectifier.

I wouldn't own a boat without an onboard charger. All my power problems went away when I got my first one. I do carry a set of jumpers as a just - in- case but since I got an onboard I've never needed them.

Jumper go in the car for the winter.

J Francho, what´s the rectifier?? would you have a diagram or something? and how do i know if it is bad or if the problem is something else??

and, the problem is that i leave the boat on an alley besides my house, not in a closed garage... i have had it like that for more than 1 year, and nothing has ever gotten stolen, in fact sometimes i leave the batteries on the boat for a couple of weeks, but i dont want to risk it... i prefer to remove everything i can, and then, one night before going fishing, charge the batteries with a regular charger.... i leave the padlock keys on top of the charger so i dont forget to put the batteries in the boat... its not too comfortable since they are heavy and i have to carry them several yards, but it is still better than having them stolen... maybe now with my restoration i can make a lockable place to put the batteries in the boat and leave them there....

so, how do i check my charging system to see if it can be fixed??

I wouldn't know where it is on your motor. It's like an alternator, it charges the battery. All I know is I've had one replaced. I don't recall it being terribly expensive.

thanx. i will have to look for a diagram or something. or i will have to invite an electrician friend of mine for a fishing trip, so he can check the motor while it is working....

Your motor probably does have some kind of charging system, but you have to run the motor a long time to put anything back into the battery, especially if your using a trolling motor also on the same one. The motor won't put enough back in. Like everyone else said, use one for the regular motor and a separate deep cycle for the trolling motor.

Most (maybe all) outboard charging systems won't produce enough to keep a TM battery charged unless you run for hours at speed. Your batteries should be different types for the cranking system and the TM. I have had several boats with only two batteries and did not have a problem . Use the cranking battery only for cranking the outboard, depth sounders, bilge pumps etc. and the other a deep cycle for the TM. Unless you don't recharge as soon as you get off the water you should not have a problem.