Bests & Worsts Reviews from Amazon

I have owned a Roomba 550 since nearly four years ago. The original battery pack became useless after about 18 months. Next, I bought a HQRP APS Battery which lasted 27 months. By the time this second battery pack also died, I feel that my Roomba is already near the end of its lifespan, so I was not going to spend a lot for the third battery. This Tenergy Replacement Battery for iRobot® R3 500 series was among the cheapest I can find, which is why I decided to try my luck and purchased it one month ago. The battery pack I received actually says '3500mAh' (or 3.5 Ampere-hour) on it, which is a nice surprise since Amazon description says just '3.3Ah'. Unfortunately, I just tested the runtime today, and it is now painfully evident that this battery's capacity is nowhere close to advertised. - The original Roomba battery (rated 3Ah) can run my Roomba for about 2 hours when new. - The HQRP battery has a runtime of about 2 hour 20 minutes, which is consistent with its 10% higher capacity rating of 3.3Ah - This Tenergy battery can only run my Roomba for 1 hour 45 minutes, or just 75% the runtime of HQRP battery. This would suggest that its capacity is only around 2.5Ah, instead of '3.5Ah' as advertised. Basically, this Tenergy replacement battery is yet another example of "You get what you pay for". Knowing what I know now, I should have ordered another HQRP battery instead. It is still too early to tell whether this Tenergy battery will remain in service for years, or die a premature death. But given that the manufacturer exaggerated the capacity number, I'm not optimistic. I will update my review in the future when necessary. [Update on May 11, 2012] I just noticed another tell-tale sign on the real capacity of this Tenergy battery pack. In the product description it says: "Max. Discharging rate : 10 C at 24 A". That implies its capacity is just 2.4Ah, so ten times the current is 24A. [Update on Mar 7, 2016] I’m happy to report that the Tenergy battery is still running strong after nearly 4 years (granted nowadays I only use my Roomba once every week). So although this battery may lack in capacity initially, it offers better longevity in the long run. I have now changed my rating from 3 to 4 stars.