I have about 100 eneloop AA and was wondering how many would be needed if someone built a starter using them. Or a trickle charger using them you could use where electricity wasn’t near.
envelope? 
I hate auto correct. Gonna fix that.
Cold cranking a diesel engine requires about 800 amps, ideally 1,000 / CCA.
Now, a gas engine in the summer will require significantly less, assuming 1C being 2A per cell on those eneloops, it might work.
Not sure what the max discharge current is for AA Eneloops.
could be higher.
Ah, well at least you know the right word, and it was just auto correct.
Imagine if someone thought that their batteries were actually Envelopes. 
I’ve seen people start fairly large outboard boat motors with a bunch of alkaline D cells.
Also does anyone know of a battery powered charger for car battery?
"Using nimh to jump start a car"
What does the national institute of mental health have to do with jump starting cars?
Hobby charger with c.12v input and Pb charging capabilities
NiMH nominal voltage of 1.2V so would need 10 in series to get 12V.
Rough estimate of CCA required for a gasoline car in the summer is 150-200A.
If we can get 4A @ 1.2V from a single AA Eneloop then we’d need 50 parallel banks of 10 cells, so about 500 cells.
In conclusion, I don’t think 100 cells will do the job; it might work to restart an already warmed gasoline car.
Ummm, the idea isn’t to use the aux battery itself to directly crank the engine, but to dump enough current into the main battery to boost it a little (hence the “wait a while before attempting to start”), then keep it attached when cranking for what little extra oomf might be needed/helpful.
Most informative answer.
Unfortunately, starter batteries are specifically designed to provide short bursts of high current and nothing else.
Eneloops are not.
However…… I would enjoy testing the limits of those batteries as Eneloops can be considered the “pinnacle” of the NIMH chemistry.
I’ve heard of people pulling 15amps from a single cell.
Do 10s5p and make those suckers pull 40 amps each!!! I might actually work if you use it like a “jump starter” because usually the Lead Acid starter battery has at least some juice in it.
They aren’t lithium, so worst case is all 100 cells will get really hot and have a drastically shorter life.
In any case, you would have to build a pretty stout pack with as much thick copper as possible to reduce resistance.
I wish I had 100 Eneloops…
That’s just AA have about 80 AAA. Try to pick all my devices around them.
Hey, my car uses NiMh to start the engine. Of course, it’s a Prius, so that’s 250V of prismatic cells… The current spike is also still noticeable if I’m monitoring the battery current at the time…