# Why Lead batteries do not need balancing?



## kennybobby (Aug 10, 2012)

flooded lead acid batteries are charged up to 14.4 at which point they start gassing and 'boiling' off, but the electrolyte can be refilled and topped off, and they are good to go--that is essentially top balancing.

trying to charge weak or old batteries, or SLA in which the electolyte level is low or unknown will not likely be successful.


----------



## jumpjack (Sep 9, 2012)

Who talked about flooded? They are 4 SLA, i.e. - *silicon* lead acid: no liquid, only silica gel, and a sealed case.


----------



## favguy (May 2, 2008)

I've never heard of silicon lead acid !! But if they are AGM's often referred to as SLA they absolutely have to be top balanced, either by current shunts on each battery or a current shuttling system. This is if charged with just the one charger. 

Why did you think they don't need balancing?


----------



## jumpjack (Sep 9, 2012)

favguy said:


> I've never heard of silicon lead acid !! But if they are AGM's often referred to as SLA


As far as I know, SLA and AGM are different technologies, and SLA means Silicon Lead Acid (vs Absorbed Glass Mat)



> Why did you think they don't need balancing?


Because there is no balancing system on my e-scooter! Just 4 batteries connected in series, and that's all.


----------



## EVfun (Mar 14, 2010)

jumpjack said:


> I have an e-scooter equipped with very old SLA batteries, quite unusable.
> Yesterday package was at 48.8V; after one night charging... it's at 41.1V...
> And this is not all:
> The *newset battery is at 12V, but the others are at 7, 9 and 11 V! *(regardless of decimals).
> ...


You have just demonstrated that they NEED balancing. You have also explained why such a function is seldom included by the manufacturer. 

You should replace all the batteries in a Sealed Lead Acid (SLA) pack at the same time with new cells from a single manufacturers lot and initially manually balance the cells. Thereafter you can *mildly* overcharge the pack regularly to maintain balance. It is possible to overcharge lead acid batteries slowly, a few percent, without damage. Excess overcharge will cause the plates to shed active material.


----------



## mizlplix (May 1, 2011)

They require an SLA specific charger to match the cell charge needs. 

I have an E-Scooter too. I charged the cells individually then in series in the scooter. I have to do that once per year to keep the pack fairly balanced.

If they all are of the same age, they should stay pretty well in balance though.

I killed a earlier pack trying to just boil them to top balance. Those small cells are fragile.

Miz


----------



## Siwastaja (Aug 1, 2012)

jumpjack said:


> I have an e-scooter equipped with very old SLA batteries, quite unusable.http://liionbms.com/balance/index.html


You have a myth here. They do need balancing and a lot of it.

In fact, sealed lead acid batteries need very strong balancing on every charge cycle --- in order of 100 to 1000 times stronger than what li-ion needs.

6-cell (12V) SLA is the biggest usable unit that can balance itself through the slow recombination of H2 and O2, but even then you need to regulate voltage and current very carefully. Series 12V batteries each need their own cell module which needs to provide powerful shunting. Separate charger for each 12V unit is another possibility.

Lower cell count is of course always better, so use 6V units (3 cells) if possible.

Traditional flooded lead acid batteries can go without balancing but will then need regular maintenance (adding water). Even then, excess boiling is not good for their life.


----------

