Solar charge controller.

[Sander]

We would appreciate any help in choosing a charge controller for a solar panel setup.

5 90W Panels (20 years old).
8 4D Batteries (4 years old).

Thank you.

[john61ct]

Victron SmartSolar 100/30

assuming the panels are all the identical model.

Going with multiple smaller ones using 75/10 or 75/15

will be best if different panels

and even if the same, give slightly better performance in the event of partial shading, differing angles

the ideal being 1:1

at a cost of extra space and wiring required.

[Sander]

They are all the same model.
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Everything else you said went over my head. Please explain

[john61ct]

Google for the data sheets & user manuals for the models I mentioned, read them and google some more to learn the terminology.

Check out the pricing for the big one vs the smaller ones

PKSYS and Bay Marine are quality vendors.

One big one or 5 little ones?

Your batteries are likely to need replacing soon, when the time comes post a new thread here.

[Sander]

Panels and batteries came of a traffic sign trailer.
The batteries were installed 4 years ago, and never used after that. They had a good charge when we got them.

[john61ct]

Lead requires sitting at true 100% SoC for longevity.

If they've been regularly topped up while stored to offset self-discharge, they might still have some lifespan left.

Only a CC load cap test will tell SoH% accurately, but rough tests might be good enough.

In any case they are unlikely to last that long even when new, not being true deep cycling type nor particularly great quality.

Maybe if they test OK as Starter batts (garage type load test), see what you can get for them secondhand?

Then buy proper new deep cycle batteries, not much pricier per Ah than the automotive / big box deals, which are 99.9% fraudulently labeled.

The best value by far is Duracell (actually Deka/East Penn) FLA golf cart batteries, 2x6V, around $200 per 200+AH @12V pair from BatteriesPlus or Sam's Club. NAPA relabels it here: https://www.napaonline.com/en/p/NBP8144 Deka self-labeled also sold at Lowes.