For 48V20Ah lithium battery, it is better to use lithium iron battery. The good price is 3000-4000 and can be used for 3-5 years. The average price is around 2,000. If you are lucky, it will last 2. -3 years. Typically this will last 1-2 years. However, if the seller guarantees it, it can be used for more than 3-4 years.
Please note that it is best not to use lithium manganese batteries, as lifespan is not guaranteed!