I'm debating between a lithium battery, and a light-weight AGM battery. The advantage of the lithium is of course the extreme light weight, but they're also quite expensive. They're also more susceptible to losing power in the cold, so if you live in an area where there are cold winters (i.e. snow and ice), you'll have to be diligent about keeping it on a tender. The AGM batteries aren't quite as light (although not bad), but they're about half the cost of lithium, and they do much better in cold environments. I guess it depends on where you live.
It seems to be difficult to get specific info about the Platinum battery, but here's the equivalent spec Duralast:
View attachment 26027
As you can see, it weighs 46.9 lbs.
Braille Battery makes a Group 8 size LiOn equivalent that weighs only 19.9 lbs, but it's also quite expensive:
The I48CS model is a standard height lithium upgrade for vehicles that are equipped with a Group 48 battery. This model has DOUBLE the power & capacity of the ultra lightweight CE & CX models and all versions have been used in hundreds of Porsche cars ranging from Cayman GT4 to variety of 911...
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$1,899 to save 27 lbs seems like a lot. The benefit there would obviously be the weight, but it's also the same size as the factory Emira battery, so it should be a straight swap without fitment issues. They make lithium and AGM batteries that are much less in weight and cost, but you'd have to come up with a mount. I don't know what the battery mount in the Emira looks like, but I'm sure it would be doable. The important spec to look for would be the Ah (amp hours) if you think your car is going to be sitting for days without being run. If you can put your car on a tender each night, you can save a lot of weight on some of the other batteries and the cost is half or less of the cost of the Group 8 size one.
This one for example costs $569.99, weighs 6.4 lbs. but it's smaller (need a way to adapt it to the factory mount) and has just over half the Lithium Amp Hour (Lithium equivalent to AGM Ah) rating at 45.
Due to extremely high demand and large orders of our lithium batteries, production lead time is 3-5 business days. We are expanding our production capabilities and will get products out as fast as possible. Thank you for your understanding. At only 6.4 pounds, the GreenLite G30 is an...
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Maybe some of the enterprising members here who have access to 3D printing technology can devise an adapter for the Emira. Being able to save 40 lbs with that battery for that price is a pretty good cost per weight-saving value.