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I've got a set of small deep discharge lead acid batteries (7ah @ 12v) and a few larger ones that I use for running electronics in remote areas for hobby use. I don't use them evenly throughout the day, so they end up at varying levels of charge as time passes.

I have a pair of solar panels and an MPPT charging controller designed for lead acid batteries. This is all well and good but the charge controller can only charge one battery at a time in this situation (though the controller does support 24v operation, I can't charge batteries in series because they're either different capacities or discharge levels, and I'm not sure it's safe to try to charge them in parallel for similar reasons).

Has anyone needed similar hardware? I don't really want to run an mppt for each battery (for 7ah batteries it would practically be cheaper to just buy a new battery every time one drained) but I haven't been able to find any hardware which has independant charging functionality, even the really high end ones seem to be designed for a single bank of batteries. I couldn't find anything designed to run a fixed dc output from which I could run a discrete charger, and I'm hesitant to run an mppt ac inverter due to efficiency concerns, and complications of tie in systems (this would need to run standalone, and most importantly, portable)

I'm also tempted to grab some LiFePO4 batteries because they're lighter and have longer livespans than lead acid, so it would be convenient if any recommended hardware could properly charge both chemistries (my current mppt does not support this).

Speed is also important to me, so anything capable of utilizing as much as possible of the output of the solar panels (200 watts total under ideal conditions) to charge all of the batteries in as little time as possible is preferable.

Can anyone make any recommendations?

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Since you're wanting to charge a variety of batteries, with potentially differing numbers charging at a given time, your "best bet" would be to connect several buck-boost converter based (or fluback converter based) chargers to the MPPT unit, and have each one charge a single battery.

With all PbH2SO4 chemistry batteries, you could easily enough build your own converters to output fixed current (or potentiometer-adjustable current) output @ 9V-14.2V (or whatever your battery mfgr recommends for float voltage) using any of a large # of available converter control ICs.

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