The Boating Forum - Batteries

I have a boat with two house batteries, charged from shore power. I have one heavy duty battery only for cranking the engine only. Is the cranking battery usually charged from the alternator only, or usually from shore power as well? I'm curious because the boat wasn't used for a while, and it started immediately, but the low battery light came on.

Thanks guys.

first i would have the same batteries,how do you use your batterty switch when running..

It's all going to depend upon how it is wired-follow the wires to find out. If the boat wasn't used for a while, the starting load could have brought the battery down low enough to have the light come on. Did the light go off after the engine was running a while? How old is the battery? When was the last time you checked it/added water (if flooded batteries)?

Captain Electric - 10/11/2006 9:09 PM

I have a boat with two house batteries, charged from shore power. I have one heavy duty battery only for cranking the engine only. Is the cranking battery usually charged from the alternator only, or usually from shore power as well? I'm curious because the boat wasn't used for a while, and it started immediately, but the low battery light came on.

Thanks guys.

maintaining a good batt system

It's definitely a whole system that matters. This may sound like overkill, but not for me when I am offshore. Here's my receipe for a robust , rugged, dependable electrical storage system.
1. AGM battereies in a quantitiy that none are drained more than 25% in any situation.
2. All batteries replaced every 3 years no matter what the condition.
3. A 3 stage smart charger that is powered on and connected to the batts 24/7 - anytime the boat is not being used, the charger is maintaining float level
4. A dash mounted battery monitor gauge that tells me when I should switch batts to fresh ones, again to not deplete any one battery too much. I use a Newmar DCE Energy Monitor.
5. Battery switches in off postion anytime the boat is in storage.
6. Miantenece of all terminals every 60 days - all terminals loosened , cleaned and dielectric grease reapplied
7. Nice addition: a battery combiner between banks that connects all the batts when it sees any type of charge (engine or shore) and charges them all. This allows you to troll with one battery and charge the entire system.


And everyone needs to read "The 12V bible" - get it on amazon....

Cranking batt should be charged from the alt & shore power

House batts should be charged by the alt (connected to cranking batt via a combiner) and shore power