Ran a group 31 deep cycle interstate with a basic solar charger system that came with the lift motor box for years with no issues on a hydraulic lift. Would raise and lower the lift nearly every day, sometimes up and down 2/3 times. If you have access to power and lift motor is 12v just run a battery charger if solar isn’t keeping up. No need to over think it with lipo batteries. 

Just curious why you didnt consider a 23 M220 as there are lots left over from last year at a good deal. Regardless what you pick Id get an M6 minimum and if you find an LT4 I'd go bigger. Ive never heard anyone every complain and say they wish they would have gotten a smaller engine.

Check out the Beach’N Boat Drain Plug Wrench too.  I like these, because they are magnetic.  I have one stuck to my trailer in an inconspicuous place at the back of the trailer. so it is always available.

https://a.co/d/cX2AzzV

12 hours ago, justgary said:

LiFePO4 will get damaged with significant charge current when below about 32F, but I seriously doubt the lift will be used then.  Note that discharge is OK when cold.  Since the battery will most likely be full when it gets cold, charge current will be very low.

Yes, quality of the BMS matters.  JBD makes 200A and 300A versions with temperature control (e.g. to run a heater blanket when the temperature drops, if desired). 

LiFePO4 will allow full discharge, where lead acid is considered fully discharged at 50%.  In other words, you can get about 50Ah from your 100Ah lead acid, but you can get 100Ah from a 100Ah lithium.  Lithium also has a much lower internal resistance, so the voltage doesn't sag much at all under load. 

The honeycomb comment/bad cell advice is wrong.  You will definitely know if you have a bad cell because the battery voltage will drop, just like it will with lead acid.  Besides, the BMS will report actual cell voltages to you if you care to see them.

If choosing lead acid, I would always go with wet cells over AGM in any non-portable situation.  The ability to check specific gravity and add water are definitely a plus when trying to keep the batteries around for a long time.

As always, do your homework before you buy.

Cold: problem is a lot of removals don't happen up north especially MN/Canada until its below freezing. There was a company 2-3yrs ago promoting LiFePo4 for lifts and a dealer sold a bunch when they were $600-750 each and they had a lot of failure only to find the battery mfg wouldnt warranty them. 

LiFePo4 are great for certain applications as you said you get about 2X more useable capacity from a "similar" sized battery where lead acid the rule of thumb is you can use 50% of the battery, and for heavy use trolling motor guys that drain frequently the DOD chart on those doesn't look pretty especially when LiFePo4 is pretty much full discharge in the avg of 2000-4000 cycles depending on cell grade! crazy awesome! as you said the voltage remains high so they are great for Kids power wheels! and trolling motors! 

Honeycomb: 10yrs ago when these started to come out they were giant cells configured in 4S (4cells in series) they could handle 100's sometimes 1000A discharge. Sadly most from overseas had a lot of poor cell quality at best and they were still crazy money. Mfgs started running a lot of 4P4S packs so that if one cell within one pack dropped you still had 3 other packs and most consumers would never know (same voltage) just less capacity. i visited many battery mfgs overseas and the main issue was "warranty" they basically all had to change into a new company every few years **still the case for many! . some of the newer ones are going back to the 4S (NO-P) so yes your correct you would know when you get a bad cell. 

i've been tempted to upgrade the boat battery to LiFePo4 but due to starting current i've been looking for one that has a 200A BMS at a reasonable price, ive found the Li-Time units have one thats 150A that i've considered trying, 

For boat lifts they are still way overkill as you simply don't need the capacity: 

* most vertical cable lifts running a gear motor: you can get by with small AGM lawn mower size batteries, or wheel chair batteries, you dont even need a grp24 let aline grp27+, your only using the top 50-10% of the battery at most any given day, granted some heavy users may use more and may have undersized solar to keep up with it.

* most Air assist boat lifts (of the past) use inverters: the inverter is ON all the time draining a ton of power so they need huge solar systems and larger battery systems, there are now PURE DC 24v blower systems that use nothing when not in use. 

* Hydraulics are gaining popularity due to wake boat sizes/weights and speeds, being on average 3-10X faster than traditional gear lifts they do use a TON of power! so even know the run time is short the power use is significant to where you want a slightly larger solar panel to keep up. on the small end hydraulics are around 150A, at 12v and 24v, however many 24v lifts are in the 180-230A range and some big boys are running 240-260A at 24v yes 6kw+!!! crazy. for hydraulics the larger the battery the better to minimize voltage drop as much as possible. some of those 6kw lifts are using 2S2P (4-monster grp 31 batteries!) talk about some $ to replace.

Sadly due to regulations most battery plants left the states and the good ingredients became a slight problem with the good ol EPA. one famous brand that use to be one of the best is now one of the worst as they come from MX and have a lot of tin/aluminum inside. funny enough they are sold on consignment especially in the marine industry. For fun if you know this brand go into any marina and check and you will see they are already way low on water due to self boiling out from excessive tin/aluminum. when the water gets low and you hit them with a hydraulic boat lift (high load) the cells short out. They show good voltage until you hit the lift and then they drop to 5-6v under load (cant pass load test) sometimes they are known to "blow up" and get acid all over. this has happened on a few boat lifts and acid splattered all over in some boats.  

ive been contemplating this one for the wake boat primary; https://www.litime.com/products/12v-200ah-plus-lifepo4-battery  or i may go slightly cheaper with two sepearte 12v-100A models and wire in parallel. ive used this brand to upgrade our shops Floor scubber and so far its incredible just not sure about dropping the $$ but they have sure come down in price!

31 minutes ago, redrooster said:

There must be something better than wood!!! 

Several manufacturers here in the south have started using juniper instead of treated pine.  It is strong enough and very resistant to dry rot and wet cycling.