Uniden introduced the radio with the small battery and later gave (at no charge) everyone the larger battery and cover because, according to them, they had always intended something in the range of 8 hours of battery life. While everyone was hard pressed to find a configuration that would allow for this, most were able to get around 6 hours out of the larger battery... and that’s pretty much how it stands today.
When the radio was first leaked to the public by one of the distributors, it had listed as an option, a AA battery sleeve to be used with disposable AA batteries. Clearly, Uniden had not factored into the original design the additional power a “software defined radio (SDR) consumed and after realizing AA’s weren’t going to make it, switched over to a rechargeable lithium-ion battery. But the optional AA sleeve apparently wasn’t removed from the info provided to distributors. It’s my understanding distributors were instructed NOT to release this preliminary info on the SDS100 but one distributer apparently didn’t get that memo!
It appears Uniden used an “off-the-shelf” radio case they have for another product they sell, a marine band portable transceiver. It’s my belief that is where Uniden’s SDS100 battery issue started. They were then forced into modifying the case to hold a battery, or battery case, that allowed for the physically bigger LI-Ion battery.
But there are still some who have the smaller battery and prefer the smaller form factor. I guess they don’t mind swapping out battery packs every 3-4 hours... or are content to tolerate it. I still have my smaller battery and have thought about picking up another one... until I realized I’d need to carry 3 spares to get me through one day at an air show! As it is, I carry a spare large one in a leather case on my belt... that’s enough for me.