zombie: How should we charge pseudo-deep-cycle lead batteries?

[zombie draft from Dec 2020, going to post as-is in case there’s any value in it]

This has been on my mind for about a year but someone finally waved the question in my face.

I’m not recommending people use pseudo deep cycles; in this scenario the OP was already lured in by Clever Marketing and already owns the turd.   How might we polish it?  Let’s review.

• deep cycle - thick, heavy plates stabilized with antimony (for example)

  • PRO:  tolerant of deep cycling (1000s of cycles)

  • CON:  high rates of self-discharge due to use of antimony.  Needs to be charged fully/regularly at relatively-high voltages, and floated after charging.  Outgassing requires watering (FLA) or recombination (VRLA like AGM and gel).  Often so heavy that high-capacity ones are divided into 6v cases.

• automotive - thin plates doped with calcium

  • PRO:  thin plates allow big rush of current to start an engine.  Calcium attenuates outgassing and limits self-discharge.

  • CON:  unsuitable for deep cycle use;  will die quickly.  Prone to grid corrosion at higher voltages.

• marine - who knows;  the term is meaningless.  Maybe somewhat thicker plates, maintenance-free versions are doped with calcium and/or antimony.  Or it could just be a sticker that says DeEP SYKLE!!!.

  • PRO:  gives walmart something to sell.  Theoretically could last longer than automotive batteries in relatively shallow cycling if the plates are heavier and charging is decent.

  • CON: does not  tolerate deep cycling (hundreds of cycles if lucky).

When it comes to charging,

• deep-cycle -  manufacturers document proper charging and provide duty cycle life estimates.

• automotive  - manufactures say nothing.  We can back into an answer by looking at how commercial auto chargers work (see below)

• marine - who knows

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The Batteries are [SuperBatt Silver 9000 series S100](https://www.amazon.co.uk/SuperBatt-Leisure-Battery-Caravan-Motorhome/dp/B07T5YYB1Y)

[this was the product that inspired this post]

I’m having a hard time finding specs on them. I think SuperBatt is a distributor that rebrands existing batteries, and that they are sealed “maintenance free” batts, like the starting battery in the vehicle. Maybe slightly thicker plates. I wouldn’t expect stellar life from them, but our goal is to make them last as long as possible without any helpful info from SuperBatt.

options

Flooded and AGM charging is a known thing; the manufacturers publish recommendations telling us exactly what to do. We are winging it here with maint-free batteries.

The simplest option would be to leave the controller on the SLA (sealed) profile (14.4v/13.8v, EQ to 14.6v but no biggie). I think I will recommend this, as it’s preconfigured, probably set that way now, and pretty close to the commercial charger settings below. Water as needed.

The calcium needs lower charging voltage option would be to use AGM profile, since Vabs tends to be lower.

The alternator voltage option would be to set Absorption to alternator voltage like 14.1v but extend the Absorption duration from 120mins to 180mins to make up for the lower voltage. Float in the thirteens.

The commercial charger option (like Ctek) is to charge automotive batteries at 14.4v then fall back to 13.6.v. I assume this works or they’d be replacing batts for customers!