Originally Posted by THE TECH
If weight was a real concern, you wouldn't have purchased an E93.
I totally agree with that. E93 weight hundreds of pounds more than E90 and E92. The electric top is also another power draw. While I would not go with a little 21 lb battery, I would consider the Mini battery that weighs about 35 lbs. I ran one of those little 21 lb batteries, a Deka ETX30L that is the same as the Braille 21 lb battery, in my 99M3 and it lasted only a year of all weather driving in NH. In the more power hungry E90M3, I would want something bigger for daily driving use.
Voltphreaks looks like it has some nice stuff, but it is expensive. There may also still be issues with Li batteries in extreme cold. We sometimes have zero degree weather in NH.