My lifetime, which isn't that much longer, but 2000 cycles. These are the batteries (lithium) that power future electric cars and the required testing proved 2000 cycles to 80% DOD (depth of discharge) before the advertised capacity drops to 80%, which is still a good battery. I'll be discharging at a rate of around 50 cycles per year and I don't expect myself to live to 100.
Not advertising hype, you purchase this type of battery for the amount of cycles it can do, and they have been tested to perform at that service. Do you think Detroit would sell an electric car if they couldn't warrant the expensive battery? The Tesla S uses these batteries (a lot more of them than my 8 cell purchase) for a 300 mile range X 0.8 (DOD) = 240 miles X 2000 (cycles) = 480,000 miles on the battery pack before its capacity is reduced by 20%.
Even though expensive, for the given cycle life they are a bargain. The above pack has (4) 3.2 volt cells to make a 12 volt battery for my electric propelled kayak, I bought (8) cells for $880.00 to make (2) 12 volt batteries that will allow more than 60 miles of travel per charge.
Batteries like these were $2000 just 4 years ago and impossible to get unless you worked in R&D for a large corporation. Now the same amount of kW-hr of storage has dropped to $880 but still rather hard to get. "Lifetime" is a term I used as a 60 year old concerning myself. It is getting to the point that no matter what I post on this forum I am challenged on. I give a glimpse into the future, and the naysayers come out of the woodwork. It is a good thing progress continues on even with this forum's doubters, because with the attitudes expressed here we would still be driving with flathead engines.