This is one of the issues that I followed peviously and had been keeping an eye on my battery in my TC33D. I ran into the same corrosion problem just a couple of months ago. As my tractor is still under warranty, I contacted the dealer to get this corrected. He stated that he would replace the battery, as well as anything else that was damaged.
At this point, I mentioned that I didn't want this to happen again and wanted a gel cell battery like an Optima. We agreed that I would just pay the price difference between the standard NH battery and the aftermarket one. I waited a couple of weeks for him to locate a battery that would fit, as this thread has already discussed the lack of a suitably sized Optima battery. I'll have to look again at the make/model of the battery, as I forget what it is now that I'm in front of my computer.
My dealer had a service tech out last week to replace the battery, and he replaced not only the battery, but also the mounting tray, all hardware, and the hood latch. Quite a thorough and well done job. The only item different from the stock configuration is that the terminals on the battery are closer to the front, and therefore closer to the hold down bar, which is metal. I just need to be careful if I ever remove and reinstall the hold down bar not to short out the terminals, or it will be a very impressive light show.
I'll get the manufacturer and model of the battery shortly for anyone that may be interested.
Rich
