Let's discuss each of these in turn.

Safety: LFE batteries are relatively safe compared to other lithium chemistries. Most importantly, they are very unlikely to overheat and explode the way other lithium chemistries occasionally do. LFE batteries are also very unlikely to explore or catch on fire when they are punctured (see this video comparing different lithium chemistries under different types of stress). For those without significant experience working with batteries, LFE batteries are among the safest options available. These batteries are still made of hazardous materials though, so while a little bit of smoke is definitely better than a large fire, if your battery cell does suffer any damage at all, please make to avoid any skin contact with the battery or any inhalation of any fumes!

Inexpensive: LFE batteries are cheap, comparatively speaking. We use batteries to store power (measured in watt hours), and LFE batteries typically provide more watt hours per dollar than other lithium chemistries, and now even lead acid. XXX

Longevity: Another important component of the cost is the lifecycle of LFE batteries. A quality LFE battery used in the right conditions can last between 3000-5000 cycles (a cycle is a full charge and discharge of the battery), while only losing about 20% of its capacity during that time. Most other chemistries are lucky to get a 1000 cycles, and many do far less (though they are exceptions like LTO). So even though LFE actually cost less than other chemistries typically, they also usually last at around three times longer.

Large Sizes: If you want to store a lot of power you either need a lot of little batteries, or a few big batteries. For reasons discussed elsewhere it's typically better to have a few big batteries than many small ones. For various reasons many other chemistries don't have battery cells (the components that are combined to make a battery) easily available in large formats. There are exceptions to this, mostly lead acid and LTO batteries, and there are ways to find larger formats of these chemistries (for example reusing electric car batteries), but by far the easiest cells to find in a large format are LFE cells.

Low Maintenance: LFE batteries are generally low maintenance battery compared to lead acid. Firstly, LFE batteries have a fairly low self discharge rate, which is roughly 5% per month. This rate is fairly similar to most other lithium chemistries, and it means that if you have your batteries somewhat charged and standing by, you can expect them to hold onto that power for long period. Unlike a conventional lead acid, you don't need to make sure to recharge a LFE battery every 30 days or so. Additionally, LFE batteries can operate safely as long as they are above freezing and below 100 degrees Fahrenheit (~38 C). When these factors are considered with the fact that these cells are among the safest available, it is clear that LFE cells are often the easiest, most straightforward cells available for most uses.

Low Maintenance: LFE batteries cells are much more environmentally friendly than most other lithium chemistries because their use neither Nickel or Cobalt. This significantly reduces the environmental burden of making these batteries, so for those wish to use solar or use batteries for environmental reason, LFE are likely your best option.

When are LifePo4 batteries Good but not the Best:

Charge and Discharge Rates: Charging and discharging rates determine how much power can be taken from or put into a battery in a given time. Generally speaking, the more power you can put into a battery the faster you can charge it, and the more power you can use from a battery at time means just that, that you can use more power at one time. LFE cells are good but not great in this department. Charge and discharge rates vary not only among chemistries, but within them as well. Some LFE batteries can discharge at very high rates, but for the most part LFE batteries like to be charged and discharged between .5 -1 C. This means that LFE batteries can typically charge/discharge their full power in one to two hours. This is far less than some chemistries, which can discharge their full capacity in less than a minute, but it is more than sufficient in most applications. Except for circumstances where power output has to be really high relative to the amount of storage, like drones or large sound systems, LFE batteries usually don't have any issues charging or discharging at the appropriate rates.

Size (Energy Density): LFE batteries have good but not great energy density compared to other lithium chemistries, but are still much better than lead acid. Roughly speaking, a LFE battery might need to be 1/3 bigger than the most energy dense lithium alternative. For most applications, this isn't a major consideration, but if space is at an absolute premium (like in a laptop), LFE may not be the best option.

Cole Temperature Charging : LFE batteries are pretty robust, but one area that they do fall short of their peers is that it will harm the battery to charge it if the battery is below freezing. All lithium batteries perform worse in cold temperatures, but it is one thing to considered for LiFePO4 is that they can't be charged if the cells themselves are below freezing. This is usually mitigated fairly easily with insulation or small heating mat, especially as LiFePO4 batteries generate heat when they are discharged, but it is an important consideration.