Anybody have any experience with one of these?

NOCO Boost Plus GB40 1000A UltraSafe Car Battery Jump Starter

They rate it for gassers up to 6.0L and diesels up to 3.0L. I'm getting it for my SDL which is at a storage facility. It's parked in my outside stall, I have an indoor spot there where I can plug in a trickle charger. Trying to jump it with my 300D didn't work, this after hooked up for over 30 minutes. The charge is at low 11s (I wish I'd checked it before trying the jump), so I don't think the battery will die anytime soon. I'm not up on the science of how a battery can get low enough to impair its viability but I don't want to get an up close look at it. The batt is halfway new and wasn't cheap.

It occurred to me that perhaps I shouldn't be risking the integrity of my 300D alternator. Would be cheaper to buy a booster.

What worries me is shelling out $100 for this model only to find out it's insufficient when I could get the GB70 for @$200. It's rated for 8.0L gassers and 6.0L diesels. They say it's a 2000A, the GB40 is a 1000A.

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Te futueo et caballum tuum

1986 300SDL, 362K
1984 300D, 138K