I've just installed an Antigravity ATX20 in my 2014 NRS. This was listed on the AntiGravity site as recommended, but on sites like Revzilla it still lists the older, smaller and general purpose battery.
The ATX20 is almost a direct fit replacement for the stock battery, just about 1/2" shorter but width and length are similar. It was as snug fit. The terminals are duplicated front to back, a neat trick, but slightly recessed too. Weight - 3.5 lbs.
It arrived fully charged, installed pretty easy. It came with spacers to increase the height, but I left them off since there is a tangle of wires under my airbox and a little more space is a good thing. I can reach the "Restart" button by removing the airbox cover. As far as I can tell, the key fob or remote for activating "Restart" is not available yet.
I am not a experienced rider, having just hit the 2000+ mile and 1 year anniversary of owning a NRS, but it feels like the bike is more nimble and a little quicker. Taking all that weight off the front forks can't be bad.
If you need a stock battery, my old one is available.
You should have went from about 12.2 Lbs to 2.6 Lb like my EarthX - that saves 9.6 Lbs at the steering head and yes, that's a big difference in top heavy placed weight. Now if we could loose another 100 Lbs overall we would really have something - the battery is the biggest weight loss for the money available, next is the exhaust, then it gets REAL expensive with lighter wheels, brake rotors, etc. Welcome to the weight loss club !
DannyCB - Yes It's the ETX24C - EqAh 24 Ah8 with 420 PCA and 270 CCA it replaces the OEM YTX14H-BS and it's a one level upgrade for the EarthX ETX18C so more power for starting modified Revo engines. Works great, lasts long time, much less weight. Battery Management System prevents over-discharge, over charge, short circuits, excess cranking and balances individual cells in the battery.
Can't remember how I ended up with the ETX36D but it spins that motor over like a champ. You just have to be very careful with battery charger/tender choice. There's a list on their site about what's acceptable.