Installation manual

7. Getting the best from your batteries

7.1. Lead acid battery type, size and life

7.1.1. Flooded or wet cells (can be topped up with distilled water)

These are the most common lead-acid battery type in use today. They are available in a

wide range of sizes and are often the most cost effective solution.

 Light duty batteries are for cars (thin plates with lots of surface area).

 Heavy duty batteries are for trucks and boats

 Deep cycle batteries have thick plates and more acid capacity, suitable for renewable

energy applications.

7.1.2. Sealed batteries

Sealed batteries cost more than "flooded" ones but have the advantage that no topping up is

required (or even possible).

Gel cells are sealed and cannot be re-filled with electrolyte. Controlling the rate of charge is

important or the battery will be ruined.

Absorbed Glass Mat (AGM) batteries, instead of using a gel, use a fiberglass like separator

to hold the electrolyte in place. Since they are also sealed, controlling the rate of charge is

important or the battery will be ruined, but AGM are often more robust than gel.

7.1.3. Electrical terminology revised

Many people are often confused by terms such as voltage (V), amps (A), amp hours (Ah),

Watts (W) and Watt hours (Wh).

A battery will be specified according to its nominal voltage (e.g. 12 V) and its capacity in

amp-hours (e.g. 200 Ah).

Power is the rate of delivery of energy at one instant in time.

Power (in W) = current (in A) x voltage (in V)

Your batteries store energy, which depends both on power and time elapsed. Units of

electrical energy are kilowatt-hours or kWh, which equate to 1000 Watt hours.

Energy stored in a battery (Watt hours) = amp hours x volts. For example:

 A 6 V 225 Ah battery can store 6 x 225 = 1350 Watt hours (equals 1.35 kWh units)

This will have a mass of about 30 kg = 66 lbs.

 A 12 V 200 Ah battery can store 12 x 200 = 2400 Wh (2.4 kWh units)

This will have a mass of about 55 kg = 120 lbs.

Do not make the mistake of evaluating batteries only by amp-hours as this is not an

indication of total energy storage. Battery weight is often a good measure by which to

compare batteries. This quality can be used to help spot the over enthusiastic sales person.

(Note that the amp-hour rating varies with duty, expressed as a number of hours discharge.

"C20" is the amphour capacity when the battery is discharged over a 20 hour period and this

will be less than "C100".)