testing battery

What's a good way to test the charge on a deep cycle battery? I've always used a volt meter, but i"ve found it doesn't tell me what I need to know. How will I know when my battery is fully charged without ordering some fancy gadget from Bass Pro Shops?

Re: testing battery

Hi, Tee-Boy.<br /><br />You can pick up a hygrometer/hydrometer at most auto supply stores. Fairly inexpensive and very accurate.<br /><br />It measures the specific gravity of the electrolyte in each cell, provided you don't have a sealed battery.<br /><br />Even an expensive load tester cannot differentiate one cell from another, and a voltmeter is nearly useless for determining battery condition.<br /><br />Good luck.

Re: testing battery

Tee-Boy<br />I agree with JB if your battery has caps that you can remove. If it a sealed battery then I suggest you buy a good battery charger. Set it to automatic and when meter drops to zero it is fully charge. The automatics you can leave connected and they will not over charge. I have not checked hear at IBoat but would before I bought one. Wall Mart has a good series of automatic charger right now and pretty cheap. They are two or three stage and will fully charge without over charging. They also have a battery conditioning mode. Also have test build in that tell of problem like shorted cell or open.<br /><br />In your other post you talk about cheap charger of 2 to 6 amps. The problem with these is all most all are manual chargers and will over charge if you do not pay close attention.<br />I would not pick a charger less than 10 amps automatic. Deep Cycle battery have thicker plates than a normal starting battery and 10 or 20 amp charger work good. Most motor homes or camper have deep cycle batteries and are charged by the vehical 100 amp alternator. I seen a lot of batteries that fail because they are never fully charged. Even with a 10 amp charger a discharged gorup 27 battery will take nearly 24 hours to charge. Todays smart automatic will charge at full amps for only a short time. As the battery charges it will taper off to zero but still maintain a float charge so the battery reaches full charge but never over charge.

Re: testing battery

Originally posted by tee-boy:<br /> What's a good way to test the charge on a deep cycle battery? I've always used a volt meter, but i"ve found it doesn't tell me what I need to know. How will I know when my battery is fully charged without ordering some fancy gadget from Bass Pro Shops?

Click to expand...

Depending on the battery, fully charged may be either 12.65 V or 12.9 V. Fully discharged is 11.89 or 11.4 and less, respectively. After charging the battery, you must let the battery sit to remove the surface charge, the recommendation is at least 4 hours, preferably 12 hours. Then measure voltage with the meter.<br /><br />100% is 12.9 / 12.65<br />75% is 12.53 / 12.45<br />50% is 12.15 / 12.24<br />25% is 11.78 / 12.06