Charger for AGM batteries

I have 2 100ah AGM Renogy Batteries in my build and I want to add shore power as an option for less sunny times. I bought a $40 charger from Harbor Freight (would have linked it but I can’t as a new user, you could find it on google pretty easily if you care) because my batteries got low and I’m getting very minimal sun. I took them out and charged them back up in my parent’s house. I planned to return it and buy one recommended online, but I keep asking myself “why can’t I just wire this one into my system?” The ones I’ve seen recommended online are upwards of $200 and this one worked for charging them back to full. Sure, it’s slow, but if I’m at a campground overnight it should give me a decent amount of power, enough to supplement sup-par solar days. Does anybody know if this would be a bad idea? I’ve been learning a lot about batteries recently and plan to do more research so even a suggestion of direction to take or resources would be helpful.

Greetings & Welcome!

Going by price alone, I can’t quite tell which battery charger you got… What is the amp rating? I would want at least 10-15 amps with 2 batteries.

This is the one I have:

I like this one because it will automatically go into maintainer mode once the battery(s) are fully charged, so no need to babysit it. (I do though, because I don’t want my generator to disappear.)

Or I found these two at Walmart:

https://www.walmart.com/ip/Schumacher-Fully-Automatic-Battery-Charger-and-Maintainer-10-Amp-2-Amp-12V/374448020

https://www.walmart.com/ip/EverStart-Maxx-15-Amp-Battery-Charger-and-Maintainer-with-40-Amp-Engine-Start-BC40BE/438914356

I no longer have solar, and my house battery is normally charged via an isolator while I’m driving, and in the rare times that isn’t enough, I can use that battery charger with either shore power or my generator.

Man oh man, generator prices are way up!!! I only paid $99 for my inverter generator 10+ years ago. Even a year or so ago, they were available for $129, today they’re all over $500!!! Inflation, yuck.

Cheers!


“Everything should be made as simple as possible." ~ Einstein


I use a promariner which is a bit more expensive, but also probably has more charging steps and allows you to choose your battery type. (No lithium on mine). Some of these will recondition your battery which is supposed to extend life of them. Whether this really works or not who knows. I chose mine because I have used this and the previous model for years without fail. You definitely pay extra for anything labeled “marine” though.

Be careful with battery chargers. If it’s not a “smart charger” designed or programmable for your type of battery it could cause damage from overcharging. Once you boil off the electrolyte from a sealed battery such as an AGM you won’t be able to simply top it off with distilled water. Damage is done.

Greetings!

I’ve heard conflicting reports on the overcharging front, and I honestly don’t know which is true or accurate… On one side, they say that the battery will never draw more than it needs/wants, regardless of how much power is available to it. The other side says they can be overcharged.

Any clarification on this?

Cheers!


“Everything should be made as simple as possible." ~ Einstein


There’s no debate about it. Overcharging a sealed battery can cook off the electrolyte, and you can’t put it back.

A wet cell battery can be overcharged as long as you keep the electrolyte topped off with distilled water.

Greetings!

So what am I missing here? I keep reading that a battery will only pull what it wishes when being recharged. Thus as it gets closer to full, it pulls less and less as it nears a full charge.

Now that being said, I always thought that it was the regulator/controller doing it’s job… If that’s the case, then why are all these people saying the battery “pulls” the juice rather than the source “pushing” the juice?

Is this a case where they are incorrectly assuming that a battery acts the same way as an accessory which only pulls the power it needs, regardless of how much power is available?

As a side note, in this day & age are they even selling chargers or controllers that will overcharge a battery? I know my battery charger, which is over 10 years old, and claims to be a manual charger, will go into maintenance mode once the battery is fully charged. Mine still has an analog meter on it, not digital.

I love the net, but so often you get conflicting answers even from the “experts”…

Cheers!


"Be the reason someone smiles today!" ~ Van_Dweller


@Van_Dweller - Yeah they do sell chargers and controllers that will overcharge your battery. My solar controllers settings will do a boost charge once a month for 2 hours where the voltage is higher in an effort to repair the battery. I have this setting disabled for my AGM’s but as I understand they make non VRLA agms that this till work on?

As far as pushing or pulling I always assumed it was like river and the currents simply goes in the path of least resistance.

Greetings!

Marvelous… Just one more stupid thing people need to watch out for… :frowning:

Cheers!


"Be the reason someone smiles today!" ~ Van_Dweller