My Insight has less mileage than yours had and my battery was changed in 2007 by Honda. This could potentially explain the more balanced battery.
I am doing this because I have a big problem having good performance when my SOC is low. On the highway it is not really a problem because my battery is charging pretty quickly and it doesn't draw to much power. But when I P&G in city, it is always trying to do background charging while I accelerate and this cause my acceleration to be alot longer than when there is no charging. I tend to not use assist, because it drains the battery to much. When I do a costco commute after returning from a highway trip, my SOC shows 19 bars and it is drained to 4-3 bars in the middle of my morning trip... When the SOC shows 2 or 1 bars, it is always trying to charge while the engine is on.
So this is what I want to change. By starting with a full battery pack that I try (really hard) to not deplete and that way I get MUCH better mpg
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It is also to extend the life of my battery, I do not have 3000$ for a brand new :P