Pretty much what the title is asking. I'm saving for a replacement battery for my 08 HCH and decided to go with a Bumblebee. They have a standard and a performance for about $400 more. Is the performance a higher capacity or does it just use higher quality cells? This is the description on their site:

To me it sounds like the capacity is the same as standard but they are higher quality cells and the pack will probably last longer? In that case, MPG might not get affected but battery life will? I doubt I'll find anyone that has tried both but if you have experience with either one, I'd like to hear how it's going for you. I'm still getting about 42 MPG with not so light driving so I'm not buying just yet but I'm having to grid charge more often and plan on buying a replacement once I can't squeeze 38-39 MPG out of mine.

 

I believe Bumblebee have an option that is higher capacity than the original pack, which might help your MPG, depending on how much highway/city driving you do, etc.

However, the quality is not higher than the original pack. The original pack used Japanese-made Panasonic/Sanyo Eneloop NIMH cells. Eneloop NIMH is much better than regular NIMH in terms of it's longevity and quality. Unfortunately Panasonic in Japan now only manufacture consumer sized (AAA/AA) and graded Eneloop batteries, not the high-amperage rated D cells used in the original pack. So the only cells available are imitations made in China, which don't last as long unfortunately. This is what BumbleBee uses, and from what I understand they stress test all the cells they receive and only use the best ones in their packs, so they're better than just rolling the dice on some cells from AliExpress.

One person reported how their Bumblebee battery pack only lasted 50k miles, compared to the original pack that lasted 150k - http://hondacivichybrid2.mooo.com/img/bumblebee_50k.jpg

 

MPG is not significantly affected by battery capacity UNLESS the capacity DROPS below the needed threshold for your particular driving environment.

A 2-3Ah battery would be fine for a mild climate and flat terrain. Put 8Ah in it and you won't see any difference. Put 8Ah in an HCH2 that does a LOT of stop-and-go driving on hilly terrain with a lot of electric A/C use, you might see a small improvement over the 2-3Ah battery, but definitely not over the stock 5.5Ah battery unless you took very scientific measurements and could detect fractions of a single mpg.

The higher capacity comes into play as it pertains to the life of the battery. As they age, all batteries lose capacity. As their capacity decreases, the % depth of cycling increases which accelerates wear and failure.