Review on Maximize Your IRobot'S Efficiency With SPARKOLE'S 5300MAh Extended Life Lithium Ion Battery For Roomba 500-800 Series by Billy Donalson

After about 6 months of good use and enjoying my roomba, the roomba would display a dead battery indicator, and constantly boot cycle when I would reposition it on the charger.I removed the battery, and decided to test the voltage. Any sane person designing a lithium battery pack will contain an electronic "brain" that manages the charge level of the batteries within. These electronics make sure that the batteries are well-maintained, so that your roomba doesn't spontaneously combust as it cleans up the cheerios your nephew tosses under your coffee table .Basically, if the charger tries to charge too much, the Battery Management System (BMS) will turn off and be like "nope, they full" and diconnect. If the Roomba is getting close to empty charge, it disconnect and say "batteries getting too low" in order to prevent damage to the batteries' sensitive inside bits.So when I went to test the voltage, I got 2.5mV volts on the battery terminals. Ensuring I wasn't insane, I use a different multimeter and still got 2.5mV, verifying my meter on my nearby drone battery which read a happy 4.09V.What this could mean, since I cannot take the pack apart (without hoping to get a replacement), are a few things:1) The BMS circuitry malfunctioned and something in the electronics died. Normally, this is rare, because in my experience the next point is FAR MORE common.2) There are 8 individual 18650 cells inside this pack. 4 in series, 4 in parallel. The BMS will (presumably) normally balance these cells so that they each have the same voltage (cells are never identical in their characteristics, so you want them all on the 'same page', so to speak). If one of these cells goes bad (aka internally shorts), then that cell will have a super low voltage and sort of tank the entire pack.For example, let's focus on the 4 cell in series case. If you have 4 cells in series (you add the voltages), they should normally be 3.6V * 4 = 14.4V if we are dealing with a nominal charge. But now, say one cell dies and can only maintain 0.5 V for various chemistry reasons. So now we have a pack that has 3.6 + 3.6 +3.6 +0.5 = 11.3V. Now remember how the BMS disconnects if the battery get too low? Well generally 18650 batteries should not go below 3.0v, so let's assume this is the minimum safe charge. This level will be 3.0*4=12V. So even if one cell goes bad, then the BMS, if simply designed (which let's be honest, they probably are not too complicated given the price), then the BMS will never charge and simply display a disconnect, as it does in my case.Honestly, subpar lithium cells are the anathema of modern devices. Given the price, these cells are probably low quality, or do not go through enough quality control in order to root out the "Early Infant Mortality" cases of the bathtub curve.Anyways, took a gamble, and I lost. Most likely subpar lithium cells. For $40, ehhhh, would probably not do it again. If you like gambling and the casino is too far of a drive, try this battery pack.If you win you get clean floors.