400 Ah of batteries in a limited space

You can squeeze 4 of these in it looks like. You probably want to cap the terminals during installation , connection and removal

https://www.solar-electric.com/fullriver-dc220-6-agm-sealed-battery-6v-220ah.html

Just what I was thinking. I don't know your access location but I was visualizing sliding them (pre wired) into the battery space off of a temporary platform sitting at the same level.

There are offerings which have an integrated BMS, such as Battleborne which are a drop in replacement type. Sure the initial expense appears to be significantly higher but considering cycle expectancy the difference is not so far apart. Additionally the energy density with Lifepo4 is ~5 times that of lead acid, meaning a smaller footprint or less weight. There is also no need to achieve full charge to maintain battery health, as lithium technology has little to no effect being at a partial state of charge. Yes perhaps the BMS is another failure point, but lead acid have equally or more potential points for failure if not taken care of properly. The advantages of electronics in automotive applications has had a fundemental impact in fuel efficiency, it's much the same in battery technology, there is always the risk of failure, albeit a very minor one, I'm sure the vehicle used dose not have a reliable but inefficient carburetor.

The change I made to LFP was the best move I've made, the lead acid bank I still have demands way more maintenance, not to say that I neglect the LFP, I do check every day, but lead acid is way more labor intensive, they are flooded by the way, AGM may be better to some degree, but they are still lead acid so still subject to the same fundemental rules.

The purpose of this post is not to convince one way or the other to the coice made, but merely to enlighten other potentially missed opportunities. My choice was prysmatic cells which require more involvement in ballancing and so forth, but this doesn't dismiss the the potential of a drop in type, which are much simpler for the average user.

This link https://www.solar-electric.com/battle-born-bb10012-100ah-12v-lithium-battery.html will lead to the description and information, there are much cheaper alternatives in the market but that's up to the purchaser to figure out.

Not sure I agree with that, LFP with a well designed BMS monitors each cell or cell group shutting down charging or discharge should one differ from the others beyond a given threshold , prevents overcharging, over discharge, temperature protection, short circuit protection, over discharge current protection and cell ballancing.

Lead acid is primitive in its basic form, even with the best controllers cells can fail, often going undetected until it's too late to reverse damage, more so with monoblock batteries where it's more difficult to remediate problematic cells. Flooded do have the distinct advantage of measuring SG, unlike AGM, but both are still the same fundemental construction. LA also requires a long absorption period to near or achieve full charge which is a distinct disadvantage in solar applications, the usable voltage range is wider, they do not tolerate partial states of charge, or discharge below 50% well.

Currently I still have a flooded LA bank in service, it has been for the most part trouble free but requires constant maintenance, mostly watering and cleaning terminals due the corrosive nature of the electrolyte. When they do finally expire, I'm prepared to spend the extra 70-80% to replace them with LFP based on experience with both.

Yes LFP dose have some limitations or challenges , especially in colder ciimates where temperatures below freezing are possible, but being in a tropical location myself that is not an issue, in fact it was the primary reason for the switch, as LA do not tolerate high temperature well, LA life expectancy in temperatures of ~35°C are cut in half, the LA batteries themselves are often in the 40°C+ in my particular case. The LFP on the other hand are usually below ambient day temperature due to the overnight cooling, on mast days often 10°C cooler.

In the end we all make our choices and pay our money, personal choice is a an individual decision based on the information available or experience gained, however experience is, in my opinion, worth more than second hand information, in other words don't take my word, try experiencing the unknown there may be a few supprises. Remember the first cell phones with a LA battery? It was commonly referee to as a brick, there would be no slim smart phones if LA technology was still used.....enough said.

The life expectancy, number of cycles, is largely dependent on how batteries of any chemistry are treated. The amount of capacity withdrawn will determine the life expectancy to a large degree, there are other factors such as temperature which play a part, this makes it difficult to generalize. To establish a baseline testing is done under ideal conditions, so while a manufacturer may claim a figure of X number of cycles, real world results will vary considerably. To make matters more confusing there are different standards used by different manufacturers, making an apple to apple comparison difficult.

The testing usually uses grid power which allows for extended periods of charging, whereas solar charging has a limited window of opportunity, this means the charging current may be significantly higher than the recommended slow charging, which will have a negative impact on expected results.

Using the cell phone example, many people change when the battery is at or near to completely discharged, if charged when depleted to 20% , the life will be significantly improved and rather than 2-3 years, it may last double that. The same applies to other uses, as a general rule lead acid life expectancy drops significantly if discharged below 50%. Lithium on the other hand allow discharge to 20% of their capacity without significant impact on cycle life expectancy. Since lithium has a larger usable range, the usable capacity is therefore greater. Should the depth of discharge be much less the cycle count could be dramatically improved with both, however lead acid has a finite life span so if not used and kept in float, they will eventually die of old age. Lithium are purported to have a much longer shell life so to speak, however either way if you're not using them you're loosing them.

This is a very complex subject without definitive answers, taking the time to study will answer many questions and create some new ones at the same time.

For a mobile application, LFP Lithium batteries are much smaller and lighter, and have less mounting restrictions than lead acid batteries, which all have to allow for eventual failure and gassing .

But LFP cells quickly start loosing capacity below 40F and cannot be easily recharged below 32F (freeze point)

LFP does require a battery Management system (BMS) to prevent damage to them