Recently I published a Youtube video going into more depth on the epidemic of batteries hitting American shores from China that are using Grade B cells (or worse). The problem with this crisis is not the Grade B cells themselves, but that the vast majority of the brands selling these batteries do not tell you that and most deliberately try to hide the fact.
I don't want to just reiterate everything said in the video. So please watch it if you are interested. But I did want to re-emphasize that every battery sold on my web store is honestly rated and any batteries using Grade B cells, such as the MillerTech SPRINTR series are noted as such. And there are other good companies out there that are also being honest, such as Sun Fun Kits, who will even send you the cell grading data from the cell manufacturer for all of the cells used in the battery they are selling you.
In the end, the decision whether to pay 30-50% more for a genuine, certified Grade A battery is up to you. Many people get away with using Grade B batteries just fine for their application. But industry experts estimate that these batteries have a 20% failure rate during the first year of use and many of these companies don't have good track records with warranty claims, especially the Chinese companies exporting to the US through Amazon and Ebay. Grade B batteries will always suffer at least minor performance issues, as well, which may not be readily apparent to the consumer. Especially if they are only seeing light duty use. But when put under high loads and properly tested by someone who knows what to look for, it is easily apparent that there is a reason they were marked Grade B and sold for pennies on the dollar to wholesalers.
So take your time, educate yourself, investigate the company or brand you are buying from thoroughly and then make the best decision you can. If you have any questions, please ask!