Battery balancers are easy. if you have 2 batteries you need 1 balancer. if you have 5 batteries you need 4 balancers. 10 batteries 9 balancers.
****What balancers do during the charging process is keep "balanced" batteries balanced.****
I believe from what I read on the powercheq site is if the batteries are out of balance something like .2 volts, the batteries still need to be individually charged until they are all equal.
If you have a series string of batteries and one is weak, balancers will not help you. During discharge the weak battery will fall out of the voltage range that the balancers can handle.
I would suggest running wires from each battery to a block (bus) on the outside of the scooter so that weekly voltage tests can be done on each battery without dissambling the scooter to get to the batteries. If you are deeply discharging the batteries it would be wise to do this everytime the batteries get charged. If the batteries don't stay balanced within the range that the balancers can tolerate, then individual chargers are needed for each battery..
Lead batteries charge in parallel just fine, they do not like to be charged in series at all. Wet cell lead batteries charge in series much better than valve regulated gel, silicone, or agm batteries because you can overvolt them during the charge cycle "and" add water that is boiled off. The overvolting in a wet cell heats the battery which helps to remove sulphate from the battery plates.
Lead batteries sulphate, this is a crystal. I have been reading here how some of us are seeing how far our batteries can go before the batteries die. Basic chemistry, you take a salt, acids not dissolved in water are called salts. Add salt to water, the salt dissolves. How do we get the salt back, 2 ways, boil the solution until the water level drops, then the, I just can't remember the correct chemical term, the moler capacity of the water is reached, the water can only hold so much acid, the acid precipitates back into a salt in a crytalized form, this is the sulphate crystals that short out and increase the internal resistance of lead batteries. Or, take water, keep adding acid until any additional salt does not dissolve.
***A weak battery in a series string is going to be boiled***.
Now that you have a weak battery, two things happen. If the weak battery does'nt short out, its internal resistance increases, pushing the charge current into the other lower resistance batteries in the string, overcharging them. If a cell or two shorts in the weak battery,, the charger may never see the terminal ending voltage to stop its charge cycle, boiling off water from the good batteries. Now all the batteries are getting boiled.
On a charged battery, the acid is in the water. On a discharged battery the sulpher is on the plates in little tiny crystals. An interesting phenomenom in chemistry is that crystals like to grow best on other crystals. This crystalization is the fundamental building block of chemstry. These crystals grow fast, in the lab we take the crystals grown in acid solutions, shine light through the crystals, split the light going through the crystals through a simple prism, shine it on a screen. We can identify the chemical structure of the crystal very easily through this process called spectral analysis. Spectral analysis is how we identify the gasses in the sun and other planets, it is how we measure the chemical makeup of the cosmos. Unfortunately for lead battery lovers, sulper and lead, they like each other, a lot. Lead crystals form very fast, I liked watching them grow in the lab. Throw some lead into almost any acid and the crystals grow rapidly. Lead paint, the lead is the pigment, different colors come from different acids and they are very long lasting pigments. Lead had nothing to do with the durability of the paint, just the durability of the color in the paint.
Back to batteries. Lead sulphate crystals grow fast. And these larger crystals don't come undone as readily as the smaller crystals, leaving some crystals behind on the plates after charging. Even a fully charged battery will give up some of its acid to the unremoved sulpher crystals left behind on the battery plates. Even more so if some of the water has been boiled out of the battery.
The moral of this story is, lead batteries are kept fully charged all of the time. As soon as you are done with even a short ride, the batteries should be charged, immediately. Deep discharging unbalances series strings of batteries. Unbalanced batteries charged in series boil off water from the battery pack. The liquid in a charged battery is acid, the acid is in the water and off of the battery plates. On a discharged battery, the acid is on the plates, where it wants to form crystals. The less water there is in a battery the faster crystals form on the battery plates that cannot be removed by charging. Battery balancers work on balanced batteries, it is much better to have individual chargers for each battery in a series string. On the small batteries used on ebikes and scooters, it is cheaper to buy individual 12 volt chargers than battery balancers.