Let's anthromorphize a bit, and consider lead-acid batteries as alive; like the family dog.
1. They need exercise; it's good for them. You get the longest life when they are worked to about 50% of their capacity at moderate loads. After they have been loafing for weeks, you will notice a distinct improvement just from giving them moderate exercise.
2. But don't work 'em till they drop! If you drive an EV until it barely moves, the batteries are having a near-death experience! This is outright battricide, and a leading cause of early death.
3. They need to be be fed regularly (charged). Feed as soon as possible after a workout; they don't like to sit around starving after use. Batteries left sitting for days in an undercharged state develop a condition called sulfation.
4. Don't overfeed, or they get fat and have cumulative health problems and so die early. Chronic overcharging is a major cause of early death.
5. Don't underfeed, or they can starve to death. Chronic underfeeding also leads to a weak sickly battery and an early death.
6. Batteries can sit unused for months (hibernate) without needing to be fed. You don't need to put them on a trickle charger; just be sure to feed them occasionally so they stay near full charge.
7. They need fresh, clean water occasionally. Sealed batteries have a built-in watering system, but flooded batteries do not. Be sure to check water levels, and fill with distilled water as needed (dirty water poisons them!)
8. They need to be kept at reasonable temperatures, that you would find comfortable. Not too hot, and not too cold. Lead-acid batteries are "cold-blooded", so the lower the temperature, the slower they get. Likewise, they can't "sweat", so high temperatures cook 'em to death.
9. Batteries can't talk. They won't whine when they're hungry, or cry when you hurt them. You have to check their state of health with instruments, like voltmeters ammeters and hydrometers.
10. There are different "breeds" of batteries, each with its own good and bad points. Slow plodding workhorse floodeds, but long lived. Racehorse AGMs that are fast and powerful, but short lived. Using the wrong breed of battery for the application, or unrealistic expectations leads to disappointing results.
11. And some is just the "luck of the draw". For no obvious reason, identical batteries in the same vehicle will have some die young, and some seem to live forever.
The usual reason you see used EVs that say "needs batteries" is because the previous owner treated the batteries cruelly. Whether by ignorance or laziness, some or all of the above guidelines were violated. But batteries are replaceable, and it usually means you can get the EV "cheap".
But such problems can be cured. A little detective work to fix the problems, and then some tender loving care will go a long way toward getting the longest life possible on the next set of batteries.
Lee Hart is an EE from Minnesota in the USA. He has been building and driving electric cars for over 25 years and is a regular contributor to EVLN The Internet Electric Vehicle List News.