(edited to correct mistakes) Lead acid works because the Hydrogen and the sulfides in H2SO4 (sulfuric acid) have a weak bond and so they easily separate and re-combine (giving up and taking in electrons in the process). The plates are close in electromagnetic balance, but they are a little off from each other. One set of plates are lead oxide, and the other inter-mixed set is lead DI-oxide.
Lead acid can put out a LOT of amps in a fairly small package (that's one of the reasons they are used to start cars), but...every minute they are being used, some of the chlorides are coating the plates, which leaves less plate surface area available to provide a chemical reaction. This means the amount of amps they put out goes down in a rapid and steady decline.
When they reach the halfway point (where half the plate surface area is covered and unavailable), then trying to draw volts will cause a deep sag in the amps. Sealed Lead Acid (SLA), should only use the top half of their physical capacity to get "adequate" performance.
Every time you charge up a SLA, some of the lead in the plates will erode away. When the plates start to develop holes, the capacity when fully charged will be less, and that is the sign that they are shot. Motorcycle batteries sometimes have a clear case and you can even see the debris/sludge building up on the bottom of the case. If the debris pile gets high enough in a given spot, it will short some of the plates. With a liquid electrolyte I believe they are called Flooded Lead Acid (FLA), I think SLA has a gel electrolyte?
For some reason, if you deep-discharge them, the re-charging process erodes the plates much more than if you charge them up at the halfway point. It is highly recommended to charge them every time you stop. If you ride to work, have a second charger at work. This is one area where 2 + 2 = 6...and I have no explanation why.
They will slowly self-discharge over time. I've heard it speculated that humidity and dust make a conductive matrix on the top of the case (I don't know). After sitting for a couple months over winter, they will be deeply discharged. And when they sit in a discharged state for a while, the chlorides will gradually crystallize, and become unable to re-combine with the hydrogen that is dissolved in solution into the electrolyte.
In a FLA, if the hydrogen in the electrolyte evaporates a little over time, the electrolyte becomes "weak", so off-grid home back-up FLA batteries are recommended to have a brief "overcharge" on occasion. What happens is that when the battery is fully charged, the excess charge going into the battery is actually electrolyzing the electrolyte-water into H2 and O2, which is why you're not supposed to smoke or have any spark or flame around a charging FLA. This overcharge re-saturates the (half water/half acid) electrolyte with more hydrogen.
1. Only use half the amp-hours (Ah), a 10-Ah SLA only provides good performance for 5-Ah of range.
2. Recharge every time you stop, the battery will last many more months that way.
3. If parking for over a couple of weeks, put it on a low-amp trickle charger.
Whether you are using 36V or 48V, I am sure there's a way to use some very cheap diodes to charge all of them with a single 12V charger (or two 24V chargers for 48V pack?). SLA will easily weigh twice as much as LiFePO4. Also, LiFePO4 will typically last 3+ years, but with 5 days a week use...you will need a new SLA pack each spring, so there is no cost savings over three years (even though a SLA pack is cheaper to buy at first, you have to replace it very often).
Why does the FLA that starts your car last over 10 years? You only drain it for a few seconds to start your car, then it is immediately topped off. Also, it is charged every second that you are driving. Engine starting FLA have very thin plates to pack as much plate surface area in the smallest package needed. Deep cycle batteries have very thick plates, but they provide fewer cranking amps (less plate surface area to work with).
