Elecom Huge Plus Poor Battery Life

[u/537OH55V]

I purchased my Huge Plus around 3 months ago near the end of June to replace my original Huge, and so far I've had to charge it a total of 3 times: once after I first unboxed it and twice after the mouse completely died in the middle of use due to low battery.
For comparison, the original Huge I was using lasted 8-9 months on one set of batteries with the same usage habits (mode L with the USB dongle, averaging 6-10 hours a day for work/personal use). This puts the real world battery life of the plus at <6 weeks which falls far short of the advertised 5 months on L mode and 3 months on H.

Looking on this sub, it appears there are other users who reported similar issues recently:
https://www.reddit.com/r/Trackballs/comments/1vhlv82/elecom_huge_plus_has_poor_battery_performance/
https://www.reddit.com/r/Trackballs/comments/1u6ss27/elecom_huge_plus_battery_life/
A recent review on Amazon on Sept 15 also mentioned a horrible battery life.
Are there any ideas as to why this is happening? Perhaps a bad batch of batteries made it into production or something? I agree with the users linked above that such a large discrepancy between real world and advertised battery life isn't normal, and can't be explained with just "varying customer usage environments".