Lead acid batteries has been around a long time and is easy to manufacture. They are rechargeable, recyclable, and reasonably safe. AGM or Absorbent Glass Mat lead acid has the added benefit of being sealed.
The reason they are so common is because of the high watt-hour/$ ratio:
- Lead acid 6.77–17.41
- Alkaline 0.48
- Lithium 2.75
They are the battery of choice for car starters, UPS (uninterruptible power supplies), commerical/industrial battery backup systems, off-grid power systems, electric forklifts, emergency lighting, etc.
Per watt-hours in use they are definitely the most common. Per unit, it would most likely be alkaline, followed by lithium and lithium ion.