There is much on this site already on this subject.
Also see Battery University and their LA and LiIon comparisons
Lead Acid (LA) can be a good choice
- where initial cost is important and
- where mass or size for a given Wh capacity is less important.
- Lead acid has better very low temperature performance than most LiIon batteries.
- In applications usually in standby with high current standby occasional use (eg UPS, automotive starting)
Lead Acid batteries will almost always be a very poor choice.
- In modern equipment that is intended to be portable and/or have good energy density.
The large majority of medical equipment, laboratory equipment, scientific instruments and portable or mobile equipment and equipment using batteries for major energy storage nowadays used LiIon.
If long lifetime is important lead acid needs attention to charge rates, proper boost cycles, limiting depth of discharge and more. Lead Acid can be a good choice for standby or cycled stationary use where size and weight are not overly important or mobile use (such as in vehicle starter, lighting and accessory use (but not usually for 'traction').
Lead acid batteries have have lower initial cost per nominal capacity but to obtain good cycle lifetimes they can be discharged to only a fraction of their full capacity.
Lead Acid have a role in emergency and standby applications where low cost is important and cycle life is less important. A UPS (uninterruptible Power Supply) may be rated at 10 kW output but be almost always in standby mode waiting the next power outage. Battery capacity will then usually be designed to provided rated power for a specified period using a large portion of the battery capacity.
High DOD (depth of discharge) significantly impacts battery cycle life if repeated frequently but in most cases a UPS may operate in standby for months or years at a time. In areas where there are frequent power outages a much larger than usual capacity battery, or even a LiIon battery may be appropriate.
LA have lower energy density by mass or volume compared to LiIon, larger whole of life cost per energy stored, more complex charging requirements and lower allowable depth of discharge for good lifetimes.
If you want even longer cycle lifetimes than LiIon at still superior performance in almost every way them LiFePO4 may be a good choice.
Lead Acid often offer superior low temperature performance (well below 0 degrees Celsius), but this is not usually a factor in instrument applications.
I also realize that many lithium-ion rechargeable batteries are labeled as smart batteries and have more communication interfaces like SMBus. My goal is to build an uninterruptible power supply with rechargeable batteries and a power management module, and wonder how much of a help those smart features would be.
Whether smart features are useful to you depends on how much effort you want to assign to the core task and how much to battery management. You have mentioned both medical equipment and a UPS. If the primary focus is implementing a UPS and volume justifies it then performing all the functions yourself using bare or protected cells with perhaps a pre-built BMS (battery management system) and any other functionality designed by you is liable to be both economic and allow you to achieve specific requirements. Batteries with "smart" facilities are often significantly more costly per Wh than bare battery based systems. This may be acceptable where an existing market price point can easily be met, but less so where the equipment must sell in a highly competitive market.
If the UPS mentioned is a sub-system for medical equipment where good power functionality is essential but is not the main role, then using what is available allows you to focus on your core task. For most applications charging and battery management requires current, voltage and temperature measurement, charge current control , battery isolation and perhaps discharge control if not part of the main task. Even with those capabilities you can implement coulomb counting for charge management, trickle up charging for undervoltage battery packs, pulse charging (if desired) and more.
ocrdu asked: (S)LA has "more complex charging requirements" than Li-ion?
Yes, perhaps surprisingly. Despite the various issues that can occur LiIon charging is usually an extremely simple and well defined process. Lead Acid charging is not.
LiIon usually uses
- CCCV (Constant Current and then Constant Voltage) charging.
- Then terminate on preset current tail.
- You can add trickle up precharging if below some preset Vmin.
Much is available on CCCV charging on SE.EE eg here and here
and much on LiIon charging here
Lead Acid batteries have different boost and float charge rates.
And various charge rates by subtype.
And electrolyte mixing and diffusion if you want to get fancy.
And differing Vfloat for deep discharge and float modes.
Also cycle life with lead acid varies greatly with depth of discharge.
And lead acid must be maintained above a certain minimum voltage as much as possible to prevent damaging sulphation.
LiIon is about as simple as they come. There is a rule set that can usually be followed to get expectable results.