Corey, like you I'm using this forum to help me learn more about ebikes before making a purchase decision, but I do have a fair bit of experience relying on battery performance. The warranty differences you mention lump a variety of variables into one number so my belief is that you are looking at apples & oranges. First is what the bike mfgr. is willing to warranty, and that's purely a business decision based on assumptions they make (about customers, kind of bike use, # of units sold, etc.) Each company will come by their own decision based on their unique set of assumptions. Then there's the battery mfgr., which is where the ebike mfgr. is getting the battery performance data which in turn they fold into their warranty decision. Battery 'performance' is about capacity, the number of amps (usually measured in so many amps for so many hours, or amp/hrs) a given battery can provide at a given voltage. Spec a higher amp load on the battery when testing its capacity and it will correspondingly produce those amps for a lower period of time. BUT it's not a linear relationship. So a battery mfgr. may do a series of capacity tests at a relatively low amp draw and produce a very high amp/hr capacity rating whereas another might test a similar set of cells & battery chemistry but test to a higher amp pull that results in a lower amp/hr rating. (They may choose different amp loads for their tests because their main customer groups are different and so typical amp loads will be different). The ratings will be different only because the test parameters weren't the same.

Another key variable is what assumption is made about the typical % discharge a battery bank sees. A common practice is to spec a battery bank such that its normal amp/hr use in-between charge cycles is only 50% of the battery bank's total capacity. And one last data point: A battery's amp/hr rating isn't just 'X amp/hrs for Y cycles' but rather how many cycles the battery can supply some percentage of X amp/hrs. IOW with every cycle of use from Day 1 the battery's available capacity diminishes slightly. So mfgrs. have to pick an arbitrary percentage below 100% and measure the number of cycles that can still produce that percentage of the battery's original total capacity. The percentage I've seen most often is 80%

This last point intersects with JoePah's comment above altho' he's coming at it a bit differently. He's saying buy a bigger bank than you initially need and then, as the bank's capacity reduces with use, you'll still have enough to use the bank for a further period. Yes, that's one way to insure a given bank will serve for a longer period of time...but the bigger bank will cost more, so it's not necessarily a more affordable option. Instead, consider how to reduce the amount of capacity you consume: If your daily commute is 28 miles RT and you buy a bike that offers, for your conditions and % power used, ~35 miles of endurance before the battery gives up, then every day you'll be consuming ~80% of the battery's available capacity (assuming a full charge). That's a high drawdown and will result in many fewer total cycles of battery performance than could be available. But imagine riding only half that distance (14 miles) and then charging the bike before returning home. Now you have two trips, each one drawing down the bank by ~40%. You'll use the same amp/hrs of capacity, but you'll be much kinder to the bank and thereby increase the number of cycles available.

Sorry about the length. People who go off the grid end up talking too much about batteries!