Stock Alternator and dual batteries

[NOTW]

Hey guys, I'm on my first boat and have a quick question. My boat came with one battery and no battery switch. I added a second battery and used a switch like this one to wire it.

So now I have two brand new batteries and I also just put a brand new oem alternator on it. My question is, if I run the boat in 1+2 I'll be running both batteries. Will my stock alternator be okay charging both batteries or should I run one battery at a time? The whole purpose of adding the battery and switch is so I could switch from one battery to the other when we stop and listen to the radio, but if I can charge both batteries at the same time with the boat running it would make it a lot easier to make sure both batteries stay charged. Thanks!

 

[badbowtie]

Re: Stock Alternator and dual batteries

I run two batteries and a switch close to that one with a stock alternator and I run mine on both batteries while under way. When I stop and anchor I switch to one battery and listen to the radio and if it doesn't want to start when I leave there flip back to both batteries and go on my way.

 

[Silvertip]

Re: Stock Alternator and dual batteries

It is not an issue. But think about this. If you know the second battery is deeply discharged, why not start the engine and then switch to the second battery. This dumps the full alternator output to that battery to get it charged rather than having to "share" the output with another battery. Unless your engine is troublesome to start, you can start the engine many many times before the start battery would need charging. Once the second battery is topped off switch back to BOTH. The switch is very versatile, take advantage of the features -- not just the "convenience". If neither battery is deeply discharged then by all means, use the BOTH setting.

 

[Fireman431]

Re: Stock Alternator and dual batteries

Both posts are correct. In addition, maintaining a full charge on both batteries is the best way to assure that your stock alternator will maintain them at full charge.

If your alternator puts out 14 volts and the both batteries are topped off at 13.2, then there is no issue with maintaining levels. If one battery isn't worth a crap and continually maintains a 11.2 volt reading, all extra current is going to recharge 1 battery.

I always put my batteries on a trickle charge the night before and never had a problem.

 

[NOTW]

Re: Stock Alternator and dual batteries

I think what I'm looking for is will it hurt the alternator? I just dropped nearly $300 for it and don't want to mess it up trying to charge two batteries. So if I'm understanding this correctly, it will distribute the charge to both batteries and may take longer to fully charge them. Obviously if one was lower than the other, it would be a good idea to flip the switch to the one that is lowest so that it can get 100% from the alternator.

 

[seabob4]

Re: Stock Alternator and dual batteries

The alternator puts out amperage. It doesn't know how many batteries there are, just as long as that amperage has somewhere to go...

Don't worry about hurting it...