How many volts should I be getting on an AGM starting/charging battery?

[vtec]

I seem to have poor luck with batteries so when I replaced my starting/charging battery I spent the money on an AGM last year. I have put it on a small charger periodically before I head out. I get on the water and drive a distance and within minutes after shutting down I have only 12.2-3 volts on my LCX25 registering. Boat sat for a week and this morning I was checking other stuff, turned on electronics to check and I had 12.2v and it started to drop within minutes. I don't think this is normal but I have only had lead acid batteries. I put it on the charger for the day and will check the voltage tonight. I will also check at the battery with a good tester.

Question is do I go back and try to get it replaced? Thoughts?

[Ozark Bob]

Originally Posted by vtec

I seem to have poor luck with batteries so when I replaced my starting/charging battery I spent the money on an AGM last year. I have put it on a small charger periodically before I head out. I get on the water and drive a distance and within minutes after shutting down I have only 12.2-3 volts on my LCX25 registering. Boat sat for a week and this morning I was checking other stuff, turned on electronics to check and I had 12.2v and it started to drop within minutes. I don't think this is normal but I have only had lead acid batteries. I put it on the charger for the day and will check the voltage tonight. I will also check at the battery with a good tester.

Question is do I go back and try to get it replaced? Thoughts?

If fully charged, wait till morning to check the voltage. Check at the battery, should be 12.7 or 12.8 on most AGM batteries( higher on the $400 AGM's). If you turn on your Lowrance it will read lower because of the load the finder puts on the circuit. .2 or so lower at your finder is normal. Lower than that means you have poor connections or wire too small. Bob

[Ltrain]

As correctly stated previously, do not go by what your graph states. Take a voltage reading across the terminals with a meter. You can also install a gauge like the dual pro delta volt gauge that not only gives you a visual led readout but also connects via Bluetooth to a phone app to give you exact voltage of your batteries.
In any case the graph will not show actual voltage of your battery

[DW]

You say you put a small charger on before you go out. You should put your charger on immediately after you come in. Further, if you are not periodically charging between uses and/or disconnecting the battery between uses the battery may be discharged.

Before jumping to a conclusion that your battery is bad consider the possibility you have a lousy charger. Test the charge profile of your charger with a multi tester. You should be reading about 14.4 volts during the bulk stage and tapering to at least 13.3 to 13.6 volts during maintenance phase. Even if you think your battery is charged and needs topping off you should charge at least 10 hours, 24 hours is preferable. The absorption phase alone tasks at least 7 hours. Old and cheap chargers don’t do this but it is hard for the average Joe to know.

[vtec]

Thanks for the replies. I went over and checked this morning and yup, got 12.6v at the battery. I turned on my GPS and it read 12.4 and then quickly dropped to 12.2. I went back and still was getting 12.6, so next question is do I have a problem with GPS unit wiring or is this common to see low volt readings on older Lowrance units?

[biggamefisher]

Originally Posted by vtec

Thanks for the replies. I went over and checked this morning and yup, got 12.6v at the battery. I turned on my GPS and it read 12.4 and then quickly dropped to 12.2. I went back and still was getting 12.6, so next question is do I have a problem with GPS unit wiring or is this common to see low volt readings on older Lowrance units?

Common because of the small gauge wire and the distance running to these units.....I never use the reading on any finder as gospel......they are just not correct. Take the resting voltage reading at the battery, resting voltage..........make sure you allow about 8 hours (overnight is best) for the surface charge to dissipate after charging, resting voltage is the true reading of battery performance.

12.6v resting at the battery is very poor! Indicates a battery at about 25% DOD (depth of discharge), resting for a wet cell is about 12.7v, AGM about 12.9v............any lead acid battery should never be discharged below 50%, at 12.6v resting on an AGM you're half way there, 12.3v is 50% DOD, 12 is DEAD.

You're not getting full performance out of you AGM, since you say it's new, I suspect the charger may not be up to the task. Many chargers have an AGM setting, different charging profile compared to a wet cell...............

On my tiller boat..........I installed an LED voltage gauge within 18" of the battery, used 16awg wire to prevent any voltage drop, I use that reading, here is a pic! I have 3 AGM's on board, the starting battery is where this gauge is hooked to, it's been sitting unused for three weeks now, still reads 12.9v !

Also, you can see how close the finders are to where the gauge is located......and they are still off by .2 or .3 !!

[muskyed]

According to Odyssey, there AGM should charge up to at least 12.85 volts after a 4 hr rest. You can not go by the volts on the locator readout. You need to read the voltage at the battery posts with a volt meter. Your locator will read somewhere in the range of .4-.7 volts lower than the actual voltage. If you are watching your voltage drop shortly after taking the charger off, that is normal for the first hr or so, that's why they recommend a 4 hr rest.

[vtec]

I really didn't charge it for long, about 2 hours, and my older charger said it was done. So this afternoon I put it on my newest charger for overnight. I will unplug tomorrow morning and check it the next day.

[yarcraft91]

When you have the LCX25 on, try changing the backlight level and see if the reported voltage is higher when the backlight is dim. That's common on the LCX27 I have.

[vtec]

I checked this morning after a full charge yesterday and got 12.85v at the battery and 12.3-4v on GPS. I didn't try the backlight thing as I didn't see the post. Thanks much on the input and battery education.