Marine "deep cycle" vs. golf cart or solar battery bank type batteries

[oldryder]

Rookie here. Presently researching batteries for battery bank. Local big box stores sell deep cycle batteries which i have used many years for trolling motors. I have always been impressed with the capacity of the batteries. These are flooded lead acid which seem the best value given I don't have an unlimited budget for this.

This installation is for back up power only so barring the end of civilization I am not expecting frequent charge/discharge cycles.

Wondering the difference in construction and/or chemistry that takes the "official" battery bank batteries 60 - 100% more expensive for a given capacity rating than the bog box store "marine deep cycle".

thanks to anyone taking the time to educate a rookie.

mark in mn

ps. if there is a good book that details the considerations for a charging system and battery bank I'd appreciate a reference. I am an engineer so it can be technical in depth. (Most of the stuff I find googling is very elementary.)

 

[namesgolden]

for my initial build I went with 4 FLA golf cart batteries to build a 200ah 24v bank. I don't plan to cycle them deep (20% or so) so they'll be a great reliable test system.

for large banks that will be cycled, only lifepo4 makes sense. ~300 usable AH's of lithium or lead acid would cost similar, but the lead acid would require maintenance, be super heavy, take up tons of space and charge slower.

lead acid needs to be fully charged every other day or so, lithium doesn't need full charges.

IMO if you're gonna build a system, you might as well use it. there's no ROI if you don't use it.

 

[Ampster]

Wondering the difference in construction and/or chemistry that takes the "official" battery bank batteries 60 - 100% more expensive for a given capacity rating than the bog box store "marine deep cycle".

It all depends on where you are standing. Last year I paid $2,000 for 8kWhr (120 Ahrs at 72 volts) of Lead Acid batteties for a GEM golf cart I was selling. That is a price of $250 per kWhr and only 50% was usable so that was actually $500 per usable kWh.
Last week, I committed to buy 28 kWhr of LFP for $125 per kWh. I am going to use 80% of that capacity so that is less than $160 per kWh.
The chemistry is completely different. The weight and size saving is on an order of three times smaller and lighter. There is a reason no EVs since the EV1 in 2000 have used Lead Acid batteries.

 

[Silentpower]

What Ampstar says...

If you are set on lead acid, and buying new, flooded in a stationary system has some advantages to sealed. They are slightly more tolerant to abuse, sealed really get screwed from any over charge. The individual cells are easier to monitor with a specific gravity meter. You cannot do this with sla or vrla. Due to over charge tolerance, you can equalise the bank which when performed correctly really helps cycle life. Problem with sealed is although the battery as a whole might read an acceptable voltage, individual cells may be different, and its difficult to equalise that out.
As for price difference, weight is the tell tale. The heavier the better really as a decent deep cycle will need to have thick plates. Many leasure batteries are starter batteries re branded. Golf cart batteries are a good choice as they are built for a reasonably abusive environment. Another consideration might be a forklift bank second hand, one advantage being that individual cells can be swapped out in case of failure.
I have to say though, that 7 years of living off 8 sealed agm batteries wore me out with constant worry about getting a decent charge over winter months. The internal resistance starts going up quickly when partially charged over time and then your precious sun energy is spent breaking it back down again. My lithium bank just absorbs all of what I throw at it, and no worrying about lengthy topping off charge... ??