I was asked about a whopper of a battery

We had a customer today ask for a larger format battery that could deliver 20 amps for 1 to 1.5 hours. That's a battery you'd rather try and carry in your pocket for sure.

And the answer to the question has changed quite a bit in the last few years. The obvious answer was Lead Acid (SLA) because that chemistry does very well delivering current and the materials are relatively inexpensive. So one can just keep getting a bigger battery until they get enough. In this case that would mean a 55Ah size.

That's about 40 lbs. worth of battery, About 400 cubic inches. That's a lot 'o lead.

And if one had a special application that just couldn't afford this kind of weight and size, then a few years ago the alternative would have been NiMH or even NiCd because the cost of Lithium chemistries was prohibitive. I'm not sure, but the Prius might still be using NiMH cells. But the cost of lithium chemistries has gone down so much that Lithium variants are the new SLA alternative.

Obviously, they've completely displaced lead acid in EV applications.

A curious note; there is an alternative that is still out there. Aviation NiCd could make a robust and smaller lighter battery than SLA. Not much smaller and lighter, but still better. But these large format NiCd cells are hard to come by. And they are prohibitively expensive. And if you try and recycle them, you'll have trouble finding a recycling center that will take them... Odd that.

And so looking at Lithium chemistries, the 2 large format types are Li-Ion and LiFePO4. Li-Ion has the advantage in energy density, but LiFePO4 has the advantage in safety and longevity. And it's energy density isn't all that bad, either. It's a lot better than SLA.

As far as cost is concerned, the two lithium chemistries are somewhat the same depending on size, current ability, and how far the cost is spread over the lifetime of the cell. In other words, if a LiFePO4 battery lasts longer, a higher up-front cost may pay off since the battery doesn't need to be replaced as quickly.

So getting back to our customer, he could either go with the ~$150 SLA option, or the ~$500 LiFePO4 option. And that ~$500 cost includes a charger because SLA chargers are common, and the customer very well might have one, but the LiFePO4 will probably require a charger since there aren't very many out there.

So what do you think of larger format alternatives to SLA? Comment below.