weak battery stupid question

[strokersquid]

One of the batteries is bad.But i do not know which is number one and which is two. i guess i can measure the voltage across them and see  if that  tells me which is bad, but is # one always in the same place and i can skip that ?

[croaker stroker]

A Hydrometer is the best way to test a battery. IMO


http://www.amazon.com/E-Z-Red-S101-Battery-Hydrometer/dp/B000JFHMRU

[fishorcrab]

Try the voltmeter after the batteries have sat there for 24 hours with the battery switch in the off position. The low one is the one I would pull to have further tested or just replace it. 

Croaker is right about the hydrometer, but getting access to each cell and then getting the hydrometer tube into the cell may be a problem.  After the battery is removed it should be easier to use the hydrometer.

If any of the cells are low, top off with distilled water and charge with a three stage charger and stress test if you want to be sure.

The bad one is likely the house battery if you troll a lot with radio, fishfinder, GPS and stereo operating plus running down riggers and crab pot pullers and your kicker does not have an alternator.   If that is the case then run a separate 3 stage battery charger on the house battery after a day on the water to keep it fully charged. My  :twocents:

Paul

[bay arima]

I notice a bad battery usually has a lower voltage reading when tested with a voltage meter. One option would be to bring the suspected bad battery to an auto parts store to get tested.

[Markshoreline]

Then, put a piece of duct tape on each battery with their correct # written on it in permanent marker!

[LvrWurst 21 SR Skip]

Stroker....I simply turned on some equipment....put my battery switch selector on #1 to see if the equipment worked. Then put the switch on #2. Found out my Stbd #1 battey and Port #2. JW

[Chuck Jones]

You can buy a really cheap voltage meter from Harbor Freight for about $5 or so..they even go on sale for around $3 or4. (or borrow one from a neighbor or friend)  Leave the batteries off the charger overnight and turn your voltmeter to DC and the range to 20 amps....then put the red and black leads on your terminals. Usually the bad battery will show a voltage of 12.5 or lower....12.75 is fully charged but when they start going bad, they read 12.5, 12.0 or in the 11's.  It's a quick test and you dont have to take them out of the storage bin as long as you can reach in to get the test probes on the terminals.  Doesn't matter which order you put the black and red leads on...if you get them on backwards, the reading will just have a minus on it but still give you the voltage.

[strokersquid]

thats what i thought thanks. got the red HF one for cheap.

[fishing eagle]

A standard voltmeter or multimeter only measures voltage. A voltmeter doesn't put a load onto a battery in any way. You can have a battery indicating 12 to 13 volts and have a bad cell. The first way you should check a battery is with a hydrometer and check specific gravity of each cell. Then you need to put a battery load test on a battery. Most auto parts stores such as Advanced Auto will load test a battery for free.

I have voltmeters or multimeter's that cost hundreds of dollars each and I would not use them to check my battery, I use my hydrometer. A voltage test is just that and proves only the battery has 12 volts or whatever; but put a load onto the battery and the voltage may be a lot less.

[ak-angler]

I'd agree that multi-meters probably aren't the right tools to confirm that a battery is good. But they can confirm that a battery is bad. If you fully charge a battery and let it sit for a day or two, and the voltage has dropped to less than 12.7 volts, the battery is usually bad (it may be salvaged with specific charging techniques). If the voltage is still 12.7 or above, it may be OK. But, it may still be bad and subsequently fail under load.

A hydrometer is much the same. It can tell you whether a battery is charged, and can confirm that you have a bad cell. But, it can't tell if you have a bad internal connection to a post, or between cells. So, again, further testing is usually necessary if the performance of the battery is questionable.

But, the original post said that one battery was known to be bad, and was asking how to determine which one it was. And for that, I like LvrWurst's answer. Disconnect one battery from the circuit and see if the problem stays or goes away. Sounds simple enough to me.