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20140629 Information Sharing: - Sealed Lead Acid Rechargeable Battery


June 29th 2014 Taipei


Dear Fidelity Measurement Friend,

Information Sharing: - Sealed Lead Acid Rechargeable Battery


Fidelity Measurement is very lucky that we have good number of customers and friends (whom we know but not buying our products) who are willing to share with us their thinking, suggestion and problem no matter these are related to us or not. Like the aforesaid customers and friends, we also share information with our customers and friends. Here we go…


One of the commonly involved subjects is sealed acid rechargeable battery used in weighing scales and indicators.


During the last 12 months, we supplied about 3800 pieces of battery separately and as spare parts to customers and friends. I asked them why they need that much battery because they did not buy that much quantity from us (sad story right?). Their answers were similar: - these batteries are needed for products of others’ but not for ours (not sure it is good or bad news to us).


Usual problems about battery they disclosed are: -

  1. High defective rate, and / or
  2. Does not last long because of reserved capacity.


Let’s try to find out the possible reasons for these in short and easy to understand wordings.


Common Reasons for High Defective Rate

High defective rate are usually caused by:

  1. Quality of battery itself, and/or
  2. Recharging is too late, and/or
  3. Method of recharging, and/or


Quality of battery itself

Besides changing to quality one, there is no good solution for this.


Recharging is too late

By nature, nearly all weighing scales and indicators present deep discharge effect to battery. When battery voltage drops below around 5.25V (I call this: - point of no return), it is very likely the battery can never be recharged again. Method of avoiding over deep discharge relies mainly on:


  • Beg and pray that users always do recharging before battery drops below the point of no return voltage, and
  • Battery recharging and protection method used … It is easy at the first glance but is a difficult subject to hardware engineers (what circuit and component shout be used to detect battery status and how to avoid overcharge) and programmers (when a product should be shut down because of lo-bat and how to avoid overcharged).


Method of recharging

Method of recharging contributes a lot to the life span and product operating time when powered by battery. Improper recharging method will:

  • shorten the life span of a battery,
  • cause overcharging. In the worst case, resulting in battery leakage or explosion.


Common Reasons why Operating time of a Battery does not Last Long

Undercharging can be one of the reasons, but it is rare. If this happens, it is mostly because of:

  • City electricity voltage drops substantially (say more than 10% than the rated voltage) thus causing the output voltage of the (transformer type) charger drops also.
  • Carelessness. For example including an AC110V adaptor to where city electricity voltage is = AC100V (Fidelity Measurement made once this mistake).


But from our past experience, major reason is usually because of the amount of lead and electrolyte inside battery…


Inside a battery, the most important things which affect output voltage and reserved capacity are: -

Plates which contents mainly lead (let’s call this lead), and

Electrolyte (let’s call this liquid)


Let’s skip voltage issue (because this is also rare case) and concentrate on reserved capacity. Provided that all other things are exactly the same, then the amount of lead and liquid together determine the capacity.


It is commonly correct that the more the lead and liquid inside a battery, the higher the reserved capacity. Here is some hint for your information (according to the data sheet of one of our battery manufacturers): -

  • A 6V 4AH battery weighs about 740g.
  • A 6V 5AH battery weights about 950g.
  • A 6V 10AH battery weights about 1570g.


In the nowadays market, it is very common to find a battery with nominal reserved capacity 6AH with weight just around 620g.


Assume that weights of all non-reserved capacity related components (like enclosure, separators, glass mat, terminals) of a normal and under capacity 6V4AH battery are the same and weigh 150g. Then it is not difficult to explain why some batteries do not last long.


Besides reserved capacity, we should also consider what likely could be the manufacturing process and overall quality of a battery produced by manufacturer who reduces the nominal reserved capacity by intention.


A good and real 4AH sealed lead acid rechargeable battery should cost not more than USD4.40 in a buying lot of 250 pieces or more. Contract your battery/weighing product supplier for more information.

Some interesting/useful information:



We hope that the above information is useful for you.


We appreciate your participation in our information sharing process and sharing with us your valued experience. If you find anything mentioned above needs to be corrected or you want to add your comments, please e-mail us.


Have a nice day!


Alvin Wu

Fidelity Measurement Company Limited

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