30A initial current limits on Pb batteries

Some lower-end AGM and SLA batteries have initial current limits printed on them and it’s not entirely clear what the limits are intended to acommplish.

AGM

The Renogy 100Ah AGM has a 30A limit printed right on the case.

So do the Universal Battery UB121000, Mighty Max 100Ah, Weize TL12100, WindyNation BattaMax, TUKOPK 100A (misleadingly called the LFP121000), and other batteries. They look and are named rather similarly and may all be the same rebadged battery for all I know.

I have seen no documentation on the limit. I suspect the recombinant materials are of such low quality and/or quantity that they cannot recombine fast enough to prevent outgassing at higher charge rates.

Outgassing == permanently decreased capacity == customer support and warranty costs.

My cynical view is these batts are a “race to the bottom” to capture the naive hashtag-vanlife market, people who don’t understand what deep cycle batteries are, how they are charged, and how they are used. Honest-to-doG deep cycles might cost more upfront but they provide more kWh/$ over their liftimes (especially GC2 and other large sizes) then 12v “deep cycles”.

SLA and other flooded batts

The warning on SLA “maintenance free” batteries is less common but may again be associated with outgassing.

My WAG, even wilder and less substantiated than the above: SLA are not deep cycle batts and are not expected to be deeply cycled. In normal use they might cycle to ~80% after a particularly hard start. At that DoD the voltage delta is not enough to get massive current. [mis]Using an SLA as deep cycle could cause big deltas, hence big current, hence increased water loss and earlier death.

Perhaps the user could pry open the cell cover[s] and add distilled water to extend life but there goes the “maintenance free!” marketing lingo. If you are going to do that

gel

Current limits on gel batteries makes sense as they can take enough current to cause cavitation and (permanent? temporary?) capacity loss.

comments

If you have solid info on why the 30A limit is there, or how gel is damaged by overcurrent please comment. I look forward to a better understanding of the issues – right now I’m just spitballing.

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