I have two batteries onboard. One is the starting battery and the other is the house battery. There is the usual battery switch selector as well. I also have a battery charger for when I'm connected to shore power. I don't use the starting battery for the 12V power onboard, just for starting the engine. My problem is that the starting battery seems low on it's charge. When I try to start the engine (Yanmar 3GMF) it does that stuttering thing like there's not enough power in the battery. If I place the battery selector to ALL or to the house battery she starts right up. Two questions: 1) I know there's a tool/instrument I can buy to check the battery power. What's it called? 2) If the battery can't hold enough of it's charge to start the engine can I replace just the starting battery without replacing the house battery? Thanks, Joe
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Try this first
before you go buying new batteries. Check and clean the battery terminals and wiring. I was having a similar problem and cleaned the terminals. A simple maintenance step saved me the cost of two batteries. But, to answer your questions. An inexpensive volt meter can test the charge on your batteries. You can find one at any hardware or home improvement store. It is an invaluable little device. You can use it to test the output on your alternator and circuit continuity also. Since you are more concerned with Cold Cranking Amps (CCA), you can change the starting battery only. Check the engine specs for the proper CCA. It is better to have too much than not enough. The house battery should be a deep cycle and there you need available amp hours to meet your 12v needs. Hope this helps.
before you go buying new batteries. Check and clean the battery terminals and wiring. I was having a similar problem and cleaned the terminals. A simple maintenance step saved me the cost of two batteries. But, to answer your questions. An inexpensive volt meter can test the charge on your batteries. You can find one at any hardware or home improvement store. It is an invaluable little device. You can use it to test the output on your alternator and circuit continuity also. Since you are more concerned with Cold Cranking Amps (CCA), you can change the starting battery only. Check the engine specs for the proper CCA. It is better to have too much than not enough. The house battery should be a deep cycle and there you need available amp hours to meet your 12v needs. Hope this helps.
Starting Battery
Mike has some good advice about checking and cleaning battery terminals. In addition, pull the three red connectors off the you main switch and clean and check them, too. I was surprised to find that one of the wires to the main switch on my boat had a loose crimp. One of the main switch terminals also had some corrosion. Both of these problems add up to decreased starting power, no matter how well your batteries are charged. BTW, I also agree that buying and using a digital volt ohm meter (DVM) is a good idea. Very handy all over the boat. But I don't think a DVM will tell you more than how many volts are in your batteries. That is useful to know and tells you a lot about your batteries' condition, but it will not tell you how many cranking amps the batteries are producing. If you are like me, you don't use your engine/alternator very much and you may not be plugging your boat into shore power to use a multi-stage charger when you leave the boat. While you certainly can replace only one battery if it turns out to be needed (test the voltage with your DVM after the battery has not been used for at least 24 hrs), it's usually best to replace both batteries with the same type. Hope this helps.
Mike has some good advice about checking and cleaning battery terminals. In addition, pull the three red connectors off the you main switch and clean and check them, too. I was surprised to find that one of the wires to the main switch on my boat had a loose crimp. One of the main switch terminals also had some corrosion. Both of these problems add up to decreased starting power, no matter how well your batteries are charged. BTW, I also agree that buying and using a digital volt ohm meter (DVM) is a good idea. Very handy all over the boat. But I don't think a DVM will tell you more than how many volts are in your batteries. That is useful to know and tells you a lot about your batteries' condition, but it will not tell you how many cranking amps the batteries are producing. If you are like me, you don't use your engine/alternator very much and you may not be plugging your boat into shore power to use a multi-stage charger when you leave the boat. While you certainly can replace only one battery if it turns out to be needed (test the voltage with your DVM after the battery has not been used for at least 24 hrs), it's usually best to replace both batteries with the same type. Hope this helps.
Joe buy the digital voltmeter
also known as a multimeter. As a general check of your start battery try the following. Leave shore power/charger on overnight. Then, with fuel shut off set the meter to 12V DC, put the probes on the batt terminals, should read 12.6 -12.7 volts for fully charged batt in good shape. Then have a buddy crank the engine for five seconds (fuel off) with probes on the terminals. The voltage will drop to around 11 volts while cranking, but if batt is good it will jump back to original voltage when engine cranking stops. If voltage stays low, that is sign of batt problem. Now start engine and put probes on the batt terminals, you should get a value of around 13-14 volts, if lower, then perhaps a charging problem. There is also a way to check the health of a batt by measuring the specific gravity of the batt eletrolite (batt water) but I don't know much about this and it is temperature dependant. Yep, you can replace the start batt without replacing the house batt.
also known as a multimeter. As a general check of your start battery try the following. Leave shore power/charger on overnight. Then, with fuel shut off set the meter to 12V DC, put the probes on the batt terminals, should read 12.6 -12.7 volts for fully charged batt in good shape. Then have a buddy crank the engine for five seconds (fuel off) with probes on the terminals. The voltage will drop to around 11 volts while cranking, but if batt is good it will jump back to original voltage when engine cranking stops. If voltage stays low, that is sign of batt problem. Now start engine and put probes on the batt terminals, you should get a value of around 13-14 volts, if lower, then perhaps a charging problem. There is also a way to check the health of a batt by measuring the specific gravity of the batt eletrolite (batt water) but I don't know much about this and it is temperature dependant. Yep, you can replace the start batt without replacing the house batt.
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