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Old 25-07-2023, 17:37   #1
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Using an AGM battery charger for lithium batteries

I just came across a great deal on lithium batteries and I'm considering taking the plunge to replace my AGMs. The only thing stopping me is my battery charger which doesn't have a lithium setting (although my solar charge controller does, if that matters).

I'm fairly handy with electronics, but my current battery charger is installed very solidly and I'm nervous about swapping out a different charger and making sure it's hooked up correctly to the battery selection switch.

What I have is this Protech-4 charger (12 volt version), which charges AGM batteries to 13.5v float charge, and 14.7 maximum. According to this article, that's very close to the maximum voltage for lithiums anyway, so while an AGM charger isn't ideal, it works OK for lithium batteries.

Is this correct? Are there any other concerns if I use an AGM charger?

Another option would be to have both battery types, and use a device to bridge the two types, but that's a little complicated for me.
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Old 25-07-2023, 17:54   #2
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Re: Using an AGM battery charger for lithium batteries

most chargers have a Gel setting that works pretty good. I personally feel using an AGM setting that goes to 14.7 way too high.

I have been in a slip for months and/just have not used my battery charger and have just let solar do the batteries
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Old 25-07-2023, 18:10   #3
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Re: Using an AGM battery charger for lithium batteries

Call the battery company with your charger's specs at hand.
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Old 25-07-2023, 20:27   #4
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Re: Using an AGM battery charger for lithium batteries

You don't have to keep LFP batteries fully charged to prolong their life like LA batteries. Leaving LFP batteries at full charge for a long time is known to reduce the life of LFP batteries, unlike LA batteries. With the LFP setting of the solar charge controller, it is sufficient to perform the required cell balancing charge by fully charging the batteries, not every day, for example every 2-3 days. It is useful to adjust the current shore charge regulator to 14.4V, which is the gel battery setting. Do not use shore charge for balancing charge of LFP battery, otherwise you can use shore charge without any problems until LFP battery is 90%Soc full.
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Old 26-07-2023, 01:06   #5
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Re: Using an AGM battery charger for lithium batteries

Lithuim will want around 14.2v. 14.7 is way too high.
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Old 26-07-2023, 02:27   #6
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Re: Using an AGM battery charger for lithium batteries

Quote:
Originally Posted by Rohan View Post
I just came across a great deal on lithium batteries ...
Consult the Lithium Battery manufacturer, on it's specific recommended charging regime.
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Old 26-07-2023, 03:34   #7
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Re: Using an AGM battery charger for lithium batteries

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Consult the Lithium Battery manufacturer, on it's specific recommended charging regime.
Per ABYC E-13:

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Old 26-07-2023, 03:55   #8
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Re: Using an AGM battery charger for lithium batteries

Quote:
Originally Posted by Rohan View Post
What I have is this Protech-4 charger (12 volt version), which charges AGM batteries to 13.5v float charge, and 14.7 maximum. According to this article, that's very close to the maximum voltage for lithiums anyway, so while an AGM charger isn't ideal, it works OK for lithium batteries.

Is this correct? Are there any other concerns if I use an AGM charger?

The ProTech-4 is pretty old. It was not an "AGM charger" per se. As I remember, it had two settings, one for FLA (and the fine print said to use that for AGM), and the other for gel. The manual has probably already told you resulting voltages from each setting.

I dunno squat about lithium, so can't advise whether the resulting voltages are good enough.

I can tell you the ProMariner's newer ProNautic chargers have something like 12-13 pre-set choices, and then you can also select specific exact voltages if one of the pre-sets doesn't suit.... so if you decide you need to change the charger, that wouldn't be a bad way to go.

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Old 26-07-2023, 05:20   #9
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Re: Using an AGM battery charger for lithium batteries

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most chargers have a Gel setting that works pretty good. I personally feel using an AGM setting that goes to 14.7 way too high.
Interesting! Thank you. My charger does have a gel setting which maxes out at 14.1v, 13.5 float
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Old 26-07-2023, 05:29   #10
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Re: Using an AGM battery charger for lithium batteries

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Interesting! Thank you. My charger does have a gel setting which maxes out at 14.1v, 13.5 float
That will work just fine. Remember that for LFP you don't need to be 100% charged like acid batteries do. So that setting will probably get to 98% and then maintain at 90% (no way to really know). But your solar is still going to charge most days so be sure to reset that controller (I have mine just doing 13.8 and floating at 13.6V currently)
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