I think I want to upgrade my old (now low capacity) AGM Grp 27 with a new AGM Grp 27 or 31. Is there a better place to find lower pricing for quality, known brand AMG batteries than Amazon? Anyone know if there might be Black Friday deals on AGM batteries (Amazon, other)? Looking at Amazon I see two seemingly decent choices with good ratings and a fair amount of raters. Any thoughts on these two in particular or other recommendations? 1) Weize ≈Grp 27, 100AH*, LFP12100, $159 Amazon, 5 Star/60 ratings. 2) Vmax Grp 31, 120AH, MR137-120, $279 Amazon, 4.4 Star/36 ratings. Since you should only run to 50% of capacity to not unduly shorten the # of cycles over the battery's life, you'd expect a theoretical 50 AH from the smaller Grp 27 battery and 60 AH from the Grp 31, right? If so, the 75% higher (+$120) priced Grp 31 theoretically gives you an extra 20% of amp hour use (60 vs 50). Is the lower priced battery the obvious choice, or is there a consideration I'm not thinking of? Of course, two Grp 27's would cost $318 or only 14% more than the Grp 31, theoretically yielding 100 AH to get to 50% SOC. I don't really know if 50% of AH really correlates to 50% SOC though. * One Amazon responder questioned Weize's rating using 10 hours, vs a 20 hour standard. Can anyone explain what that means in actual amp hour run time or affect this decision? "The standard for battery ratings is 20 hours NOT 10 hours like this battery. It is false rated to catch you if you're not paying attention and make you think it's a normal 100ah battery. IT is not, you are getting a 50 amp hour battery actually if you use the STANDARD amp hour measurement of 20 hours. Why is this battery False rated ? Is it to catch people off guard and getting half the battery they thought they were buying? see less By Amazon Customer on November 11, 2019"