Battery Care

Dead Batteries or Batteries That Don't Last Are Not Useful In An Emergency
Take Good Care Of Your Batteries!

Here is an excellent link which provides information on battery types, capacities and how to care for them http://www.buchmann.ca/toc.asp.

Introduction

Whether for remote operation, backpacking, special events or emergency use, there is a size and capacity of battery to fit all applications. What you do once you buy a battery will determine its useful life. Besides physical abuse, the two things that shorten battery life are over charging and under charging.

Gel Cell batteries are often used as a portable power source in ham radio. There are many sources for gel cell batteries, from flea markets to alarm supply stores to electronics specialty outlets. The price, size and condition will vary greatly.

The "gel cell" is a sealed lead acid battery. The electrolyte (acid) is stabilized by combining it with a gelling agent or by using an absorbent plate separator. This type of battery can usually be stored, used, charged and discharged in any position.

Some lead acid batteries are designed with a plate size imbalance or a catalyst, to help control gas generation and to aid in deep cycle recharging. These are known as "deep cycle" batteries. This type of battery is often associated with Marine use, where some batteries offer boat engine starting capacity and deep cycle capacity.

Do's and Don'ts

• Do Not charge batteries in a sealed container. ALL lead acid batteries, including gel cells, can produce hydrogen gasses.
• Do Not use an automotive type battery charger for gel cells. The output voltage is too high and will overcharge the battery. Overcharging shortens battery life.
• Do Not store a battery in a car in hot weather, under direct sunlight, in front of a stove or near a fire.
• Do Not carry the battery by the terminal connections.
• Not charge a battery beyond the time specified (if using the cycle method). If the battery is not fully charged even after being charged for a time longer than specified, discontinue charging and remove the battery from the charger.
• Do Not discharge A 12 volt battery below about 10.5 to 10.7 volts (1.75 volts per cell x 6 cells). Sealed lead acid batteries will generally not tolerate repeated deep discharges.
• Always charge a new battery before use
• Always Install insulation covers on terminals to prevent shorts.
• Always install a fuse in the cable connecting to the battery, to protect the battery and cable from shorts. Install the fuse on the battery end of the cable.
• Always keep the battery clean.
• Always charge a battery that has not been used for a long time. The battery gradually loses its capacity due to self discharge during storage. Periods over which the battery can be stored without charging are given below in relation to storage temperatures:
  • Below 20^oC: 9 months
  • 20^oC to 30^oC: 6 months
  • 30^oC to 40^oC: 3 months

Charging

There are two considerations for charging a battery; how to charge it quickly and how to keep it charged. Before building or buying any battery charger, get a volt meter first. The only way to know what is really happening with the battery, is to measure the voltage levels. This is important over time, to ensure that the charger is operating properly and to detect battery deterioration.

Rapid charging of a battery requires a lot of user care or a charger designed for rapid charging. Batteries can be damaged if they are charged to fast or too long. Rapid chargers monitor the charging rate and voltage, and adjust the charging current during the charge cycle. Some chargers are designed to go into maintenance mode once the battery is fully charged which ensures that the battery is not overcharged, but is always ready when required.

Keeping a battery charged, ready for use, can be accomplished in several ways. This same charger can typically be used to charge the battery as well, it just does it slowly, so it may take a day or more to reach a fully charged state. It is critical to understand the limits of your battery to ensure that the battery is not overcharged.

There are two options described in this document:

1. build/buy a charger
2. use a regulated power supply with an adapter

Lead acid batteries used for ham radio applications spend most of their time sitting on a shelf.

The sections below describe the types of charging available, but this section jumps in with some solutions for maintaining the battery.

Terms

Battery Cycle

• One cycle for a battery, is a discharge plus a charge

Amp-Hour Rating

• Battery capacity based on the amp-hour rating, where the current in amperes is multiplied by the time in hours that current can be drawn.
• For example a battery which delivers 2 amps for 20 hours, would have a 40 amp-hour rating.
• There are limits on the discharge current, so that a the example of a 40 amp hour battery does not mean 40 amps for 1 hour.

Deep-Cycle Battery

• This is a specially designed battery, which has thicker plates and a high density active material. The thick plates allow for reserve energy to be discharged, while not leaving the battery in a condition where it cannot be charged.
• Typically the discharge is at a slow rate, such as for a trolling motor.

Float Voltage

• A constant voltage applied to a battery to maintain its capacity. This is slightly lower than the batteries full capacity.

Chargers

There are three types of chargers for gel cell batteries:

1. Constant Current
   • A small constant current is maintained through the battery for a long period of time.
   • This type of charger is designed for a 12 to 16 hour charge time.
   • This is the most common and least expensive charger.
2. Constant Voltage
   • A constant voltage is maintained across the battery terminals.
   • When connected to the battery, there is a high initial charge current, which tapers off as the battery charges.
   • This type of charger usually completes its cycle in 2 to 4 hours and is terminated by a timer to prevent overcharging.
3. Constant Voltage and Current
   • The charge current and voltage vary as the battery is charged.
   • When the battery is connected, a moderately high charge current is supplied to the battery.
   • The voltage rises as the battery is charged and the current is reduced. The state of charging will continue until the battery is removed. The maintenance current is required to make up for the batteries self discharge.
   • Charging time takes from 6 to 12 hours depending on the batteries original condition.

More elaborate chargers will also include temperature compensation. This is required because the batteries charging characteristics vary over a temperature range.

Charging

There are two main charging methods for gel-cell batteries:

1. Cycle Use
2. Float Use or Trickle Charge

Cycle Use

With the cycle use charging method, the battery is charged to its maximum capacity and is then removed from the charger. The battery is connected to a load when required, which will discharge the battery. The discharged voltage of the battery should not go below 10.5 to 10.7 volts (1.75 volts per cell x 6 cells).

When the battery is discharged, it is connected to the charger and is charged once again. The maximum charging voltage is 14.5 to 14.9 volts, depending on temperature (See table below). The typical value to use is 14.7 volts, which is the charge voltage at 25^oC. Charging time is 6 to 12 hours, depending on the batteries state of discharge.

The maximum charging current is equal to CA, where C is the batteries rated capacity and A is the initial current rating from the battery manufacturer. The recommended maximum charging currents are:

4 Ah = 0.3 x 4 = 0.12A (120mA)

7 Ah = 0.3 x 7 = 0.21A (210mA)

WARNING: Do not exceed the maximum voltage or current and do not leave the battery on the charger beyond the typical 12 hour limit. This will cause the battery to overcharge, leading to permanent reduction of its capacity and premature failure.

Float Use

The float use method is often mixed with the trickle charge method, because both types use the same charging style. Float use means that the battery is permanently installed in the circuit with the load and the power supply/charger. When the power supply/charger fails, the batteries supply the power. This method is used by the telephone company to ensure that the phone system is always working.

Trickle charging is associated with a battery that is not connected to a load, but has a charger attached. The battery must be connected to the load when required. The charger is just that, a charger and is not capable of supplying power to the load. When the battery is attached to the load, the charger is removed.

The important difference of the float use method over the cycle use method, is that in the float use method, the battery is charged to a voltage that is below the maximum volts per cell for the battery. The typical float voltage is 13.4 to 14.1 volts, depending on temperature (See table below). The typical value to use is 13.7 volts, which is the charge voltage at 25^oC.

The battery has less capacity when charged under the float method, but it is possible to leave the charger attached without damaging the battery. This is the type of charger used in alarm systems. The charger is not sophisticated, it simply is designed not to exceed the float voltage.