Short answer is about 2 years but i have seen it go on to 4 years. it all depend of the riders expectation. Lots of variable to determine the durability of the battery. but battery do not last for ever and hence the increasing danger of the explosion if the Battery and charger is faulty.
Having said that; there is a huge price different between china local brand and oversea brand namely; Panasonic, Samsung and LG. price different is almost double in price.
Then you have the voltage from 24volt to 84volt. volt determine the release of the power which is control by the compatible controller which is determine by the finger trigger throttle. Next is the Ah which is basically the storage capacity that determine how far you can travel in one full charge. But it is still not that simple, some of the reader may understand the concept of how the voltage and amps work together.
Every responsible escooter seller will tell you not to leave the battery empty for 6 months to a few year. the battery itself require a small voltage to keep the charger charging. it is is empty for a long time, one possible remedy (i learn from you tube but have never tried it myself) is the use a bigger voltage charger as a jump start. only for 5 second and them unplug. if escooter is 48V, use a 52V charger to jump start. and start praying with swear that the battery is ok. otherwise.
Do not over work the battery. riding 40 to 60Kmph continuously for more than est. 20 minutes, can cause the battery cell to over heat. It will also overload the voltage and melt the cable. some cell maybe damage and reduce the life span of the battery. A good tell tale sign will be patch mark of the surface of the battery pack and the battery housing where they touch.
Cost of battery depend on its amps. the bigger they are, the more it cost. price range from $400 to $2000. the one in the picture is a LG 35Ah that retail at $2200. so keep those battery charging. failure to keep it charging will kill even a new battery. Warning; Warranty will not replace the battery. it can be tested and verified by escooter workshop.
Tear and wear of the battery depend on a few variable; weight of the rider, speed, length of traveled and hilly climb. You will experience the aging of your battery when the frequency of charging over a period of time increases. For example: when the battery is new, they charge once every 2 weeks, then once a week, twice a week, once a day and so forth. A typical sign of a failing battery is that once the owner unplugs the charging cable (at whatever level), the number of bars literally drops on the display panel.
Do not try to safe money of the battery for your safety sake. with the price of petrol at record high ($3.00 per liter and growing), the rider have save on tax and WOF and what else the government might impose. You may not agreed, personally i prefer that there will be a registration of license number so that we can iron out the irresponsible riders and that the responsible riders can ride in peace and safety.
please take care of your investment and be safe.