I was looking for an Optima 51R and found out they had been discontinued, so I thought I'd try this instead. This battery is a little smaller than a group 51 size battery, so I had to do some custom work for my factory battery bracket to fit. (Not sure what size this battery is classified as..)

This battery cranks the engine much harder than my stock battery ever did. I was also able to leave my stereo going for 5+ hours with this battery while working on the car. Not quite as long as my old optima, which could go 8+ hours, but still plenty good.

I've had this battery 6 months now (according to the email from Sonic Electronix) and so far it hasn't let me down once.

Other notes:
The battery comes with a metal sleeve, which I recommend taping to the battery to help make installation easier. Otherwise you have to hold the sleeve from falling out while you're trying to install the battery.

I also had to slightly modify my factory battery terminals, as they wouldn't clamp down hard enough on the battery posts, which were slightly smaller than any other batteries I've ever used.

Good battery at a good price.