Battery Issue

Hello Gator guru's

I have a 2011 825i bought new with the JD electric over hydraulic snow plow which was Dealer installed, and a small LED light bar that i added as the only add-on items i have replaced the battery nearly every year with a new JD battery as they will not take a charge or hold any longer. I have a battery tender connected at all times when not in use yet every first cold snap turn the key to nothing but clicking and dim headlights. I can jump it to start but the battery is so weak if I touch a plow switch at idle it will kill the engine. if I put in neutral and rev engine all is well "plow works" so the alternator is working.

So enough with background. my question(s) what is a good replacement battery that fits in the spot under the seat that will hold up to the low speed plowing as the JD dealer batteries seem to be a pos. I have seen optima yellow top 51 mentioned on this form any others? is there something else cooking the batteries. I should mention i have 3 different battery tenders that get used and mixed around so its not them.

thanks in advance