subject: Battery Testing Part 1 [print this page] Testing Batteries Part 1: Testing Batteries Part 1:
How to determine the State of Health of Lead-Acid Batteries
Batteries do not come with an energy gauge. Some electric vehicles and alternative energy systems come with battery monitoring devices, but it is not common in applications like golf carts, boats or RVs. This article is intended to help you determine the health of a lead acid battery.
For the testing purpose there are two basic types of lead-acid batteries; flooded and sealed. For more information on the different types of see articles: Types of Batteries and the BLS and Lead-Acid Batteries: A Basic Orientation. The most obvious difference is that with flooded batteries you can access the electrolyte or add water while with sealed you cannot.
The cycle of a battery
The State of Health (SOH) of a battery is more or less an arbitrary measure of the condition of a battery compared to the manufacturing standards. The measurement is calculated in a percentage value.
When we buy new batteries we expect them to have a full SOH, but that is rarely the case. In general, a completely new battery does not start with a 100% SOH as it takes some time for the acid solution to permeate the plates to achieve the full potential of the battery. On the other hand, batteries deteriorate simply by being stored unused. Batteries will slowly but constantly discharge during storage, causing them to deteriorate over time. This discharge produces accumulating lead sulfate, which turns into crystals that do not go away with a normal recharge. Over time battery plates become completely covered in sulfate crystals causing them to die a premature death.
Batteries should come with a stamped manufacturing date. It is not recommend buying batteries that have been sitting on the shelf for more than 6 months.
Factors influencing the SOH
There are external and internal indicators of the SOH.
External factors include rusted terminals, bad connections, cracks and bends.
A mechanical inspection is simple and informative.
1. Check if the connectors are clean and free of rust. Those are easy to clean up or replace.
2. Cracks: Any cracks on the battery body are a reliable indicator of the need to replace a battery, especially on flooded batteries or batteries than have been dropped or left without charging in regions that experience heavy winters. Letting a battery discharge during the winter will cause the solution to become mostly water which can freeze and cause the batteries to crack.
3. Bends: batteries that have been boiling tend to develop pot bellies. The positive plate on those batteries has a limited viability as they can crumble and will basically come apart. For a golf cart owner is better to replace those as soon as possible. On Solar /wind banks you can get more out of them. In any case make sure to check internal factors to make an informed decision.
Internal Factors are tied to the State of Charge (SOC), the internal resistance, the number of charge-discharge cycles and ability to accept a charge.
The State of Charge (SOC): it tells you how much fuel you have left in your battery. The SOC of a battery is measured in percentage units where 0% is empty and 100% is full, with a whole range in between. It is an indirect measurement of how much energy you have in your battery.
There are two main types of methods of measurement the SOC: The chemical type and Voltage.
1. The Chemical method can only be used with flooded batteries. You will need access to the electrolyte to measure the specific gravityof the electrolyte (sulfuric acid).
Specific Gravity or better called Relative Density is how the density of a substance relates to another one that is being used as reference. The compared substance can be more or less dense than the established unit. In our case the reference unit is water that has a density of 1.0 and our analyzed substance (electrolyte) is going o be the sulfuric acid in the battery. (See Chart 1 for details).
2. The Voltage method can be used with any battery type flooded and sealed. It measures how much electrical energy is flowing inside a circuit from one point to another point. The electrical potential that is measured in volts. It measures the voltage from the positive pole in the battery to the negative one.
The voltage is compared to the SOC of the given battery. Different battery companies have their own charts of discharge curve to calculate the SOC but in general they are similar. (See Chart 1 for details)
Chart 1. Each battery manufacturer has a State of Charge Chart that you can reference. Below is an example of a State of Charge Chart from Trojan Batteries:
