External charger question

I’ve learned a lot so far I think as I’m fairly new to solar. I have a 12v portable system with 2 6v npp 180ah agm batteries. This is for a cabin and at home just to keep the batteries maintained. I want to use an external float charger to charge the batteries at the cabin when we run the generator and also charge the batteries at home using an outlet and not the solar. I have a small 900mh charger that says it’s for agm and other batteries. My battery charging spec is 7.25v-7.5v. The float charge spec is 6.75v-6.9v. For the life of me I cannot figure out if it will be safe to maintain charge/float charge with this charger. My mind goes in to shutdown mode when I think too far in to things. If this will not be ok to do, any suggestions of charging it at my house when I’m not using it? I’m probably leaving out details that are needed, just ask away. Thanks in advance since I’m tunnel visioned and stumped on what seems to me an easy answer. I just don’t want to charge too fast.

I think you're saying you have two of these 6V batteries in series:

http://nppbatteries.com/static/NPD6-180Ah.pdf

But, you haven't told us much about the charger or your testing capabilities. Could you tell us the make and model of the charger, or measure its open circuit voltage, or provide photos showing all the text on it?

zaps said:

I think you're saying you have two of these 6V batteries in series:

http://nppbatteries.com/static/NPD6-180Ah.pdf

But, you haven't told us much about the charger or your testing capabilities. Could you tell us the make and model of the charger, or measure its open circuit voltage, or provide photos showing all the text on it?

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Yes, those are the batteries hooked up in series of course. The charger is a car quest brand and if this is not the correct or sufficient wall charger for my batteries, which kind should I be looking for? Also, I cannot find the max volts that those batteries charge to in the paperwork that came with the batteries or the battery specs. What is the max volts these batteries charge to?

That charger outputs less than an amp (900mA). You have 180Ah batteries. At half full, it would take at least 90 hours to recharge the batteries. Don't waste your time. Get a 20 to 25A charger to make it worth your time.

zaps said:

I think you're saying you have two of these 6V batteries in series:

http://nppbatteries.com/static/NPD6-180Ah.pdf

But, you haven't told us much about the charger or your testing capabilities. Could you tell us the make and model of the charger, or measure its open circuit voltage, or provide photos showing all the text on it?

Click to expand...

My testing capability will consist of turning my system on and checking the display on my epever MT50 monitor.

SolarQueen said:

That charger outputs less than an amp (900mA). You have 180Ah batteries. At half full, it would take at least 90 hours to recharge the batteries. Don't waste your time. Get a 20 to 25A charger to make it worth your time.

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Well, that makes sense. I guess I’m more concerned with the top off charge. I may not be explaining this the way I think. If I use a 20amp charger it will definitely charge way better but my understanding at a certain point, let’s say 80% charged, will a 20amp charge top off hurt the battery? Doesn’t a slow charge, for the near end of charge, charge better? Am I over thinking this? Thanks for a different look at it, now I know the 900ma will basically be doing nothing.

Delaware79 said:

If I use a 20amp charger it will definitely charge way better but my understanding at a certain point, let’s say 80% charged, will a 20amp charge top off hurt the battery? Doesn’t a slow charge, for the near end of charge, charge better?

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If you get a multi-stage charger, it will slow the output as the battery gets full. Here's an example of a multi-stage charger. https://www.altestore.com/store/cha...ge-2-20-amp-battery-charger-12v-3-bank-p9007/

SolarQueen said:

If you get a multi-stage charger, it will slow the output as the battery gets full. Here's an example of a multi-stage charger. https://www.altestore.com/store/cha...ge-2-20-amp-battery-charger-12v-3-bank-p9007/

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Thank you! This gives me viable options for my use. I see now that a multi stage charger is the direction I need to go so I get the initial 20-30amp charge then the top off charge all in one shot instead of getting next to nothing with the battery maintainer I was questioning in my pics. Appreciate everything!