There are many different types of battery you can use to power your equipment, ranging from small 6v hand held rechargeables for small busking amps to huge deep cycle RV and forklift batteries capable of powering full out door gigs and lighting systems. They all have different uses and characteristics which you should be aware of before you design your power system.
We’ll start with the smallest.
Smaller equipment such as busking amps, battery powered fx pedals, stereo’s and mixer units etc. can often be adequately powered using UK sized AA, C, or D sized batteries. If you’re out playing a lot you’ll be getting through shed loads of them so buying a decent set of rechargeable’s will save you a good deal of money in the long term. You generally have the choice of buying two types, Ni-Cd or Ni-MH.
Nickel Cadmium (Ni-Cd) or Nickel Metal Hydride (Ni-MH) ?
Nickel Metal Hydride (Ni-MH) batteries generally deliver more power for longer periods of time and can be recharged more often than Nickel Cadmium (Ni-Cd) batteries. Ni-Mh batteries are more suited to high drain applications and do not suffer from the so called ‘memory effect’.
To achieve optimum performance and sustain battery life, Ni-Cd batteries should be fully discharged before any subsequent recharge. Failure to do so, can result in the battery creating a sort of fake ‘memory ‘ barrier at the point in the cycle from which it was recharged. During future use, the battery remembers that level and only discharges to that same point.
It is also claimed that overcharging Ni-Cd batteries causes them to become somewhat ‘lazy’, affecting their ability to hold and dissipate charge evenly. Lazy batteries are prone to discharging very quickly even immediately after a full recharge. This claim is disputed by fans of nickel cadmium cells as it is said a few deep cycle recharges can often return the batteries to good working condition.
Ni-Mh on the other hand do not suffer from memory problems or issues with laziness, and can be topped up and charged at any point in their usage cycle without affecting their capacity.
I personally go for the Ni-MH.
Types of Car, Marine and Heavy Duty Batteries
There are 3 main types of battery. Starting batteries, marine batteries and deep cycle batteries.
Designed for starting and running engines, powering car lights and radios etc. These type of batteries are required to produce very high starting currents for a very short space of time and not for supplying heavy and continued loads.
Starting batteries are not designed to be repeatedly charged and discharged during normal use and should never be discharged by more than 5% of their capacity. In their usual automotive applications, any drain placed on a starter battery is immediately replenished by the vehicles’ alternator when in motion, keeping it constantly topped up and in good condition.
Deep Cycle Batteries
Deep cycle batteries are designed to deliver a larger output for longer periods of time and to withstand countless charge/discharge cycles before their performance drops to unusable levels.
A deep discharge is generally regarded as discharging a battery by 40% or more.
Deep Cycle Battery
Deep cycle batteries are designed to be discharged by up to 80% of their initial capacity, but in reality, no battery should ever be discharged by more than 50% of it’s rating on a regular basis, even if it is a deep cycle.
Once you drain a deep cycle battery to below 20% of it’s capacity, it’s inner structure is compromised and life span is considerably shortened. See the notes on depth of discharge (DOD) below to see how a battery’s lifecycle greatly depends on the depth at which it is regularly discharged.
Marine batteries – Fall some where between the two above.
As you can imagine the demands of a boat battery would be somewhat greater than that of a car and a combination of both high starting and deep cycle qualities are needed. You may often see batteries sold as ‘Deep Cycle Marine’ batteries but there is no real way of telling their exact make up or how good they are in relation to a true deep cycle battery. The term deep cycle is often overused by companies selling marine batteries.
You can differentiate a true deep cycle battery normally used in forklift trucks, RV’s (recreational vehicles) and golf carts etc. from a marine battery as any battery rated in CCA’s (cold cranking amps) or MCA’s (marine cranking amps) may not be a true deep cycle battery.
Deep Cycle Batteries Used In RV’s
Depth of Discharge (DOD) Rating
When buying a battery, be sure to look at the figures given by the manufacturer for depth of discharge (DOD).
DOD rates are important as they define the way a battery’s power capacity has been tested by it’s manufacturers.
A battery that is discharged by only 10% each time it’s used, will have a life span of up to 5 times as long as a battery that’s been discharged to a depth of 50% each cycle.
Although deep cycle batteries are designed to withstand regular discharge cycles of up to 80%, the same battery discharged by only 50% will have nearly double the life span of one exposed to a DOD of 80%.
Be aware of this when studying the manufacturer’s lifecycle figures for your battery. The lifecycle expectancy quoted for the battery you buy may have been rated at a different discharge level than that which you intend to use it. This could result in you buying a battery that in reality has a much shorter life span than expected.
Amp Hour Rating Time and the Peukert Effect
You must also look at the amp hour rating time that the manufacturers give. This is the amount of amp hours the battery kicks out when it is discharged down to a certain voltage.
Due to the nature of battery physics, the rate at which a battery is discharged directly affects the amount of amp hours it can supply. If a battery is discharged quickly, say over a period of 8 hours, it’s capacity will be considerably less than that of the same battery discharged over a 20 hour period and even more so as one discharged over 100 hours.
This theory is known as the Peukert effect. To save going into a load of technical blurb and to keep things simple, I’ve given a few examples below.
If you were to completely discharge a battery over 20 hours, it’s amp hour capacity can be anywhere from 10 – 20 % lower than the same one discharged over a 100 hour period.
A battery discharged over 8 hours can have a capacity anywhere between 20 to 35 % lower than if it were discharged over 100 hours.
A battery discharged over 8 hours can have a capacity anywhere between 15 to 20 % lower than if it were discharged over 20 hours.
It is also considered that if you discharge a battery at full whack ie. at it’s maximum amp hour rating, it will only be capable of supplying half of it’s actual (Ah) capacity.
So a 20 amp hour battery discharging by the full 20 amps in one hour, would only actually supply a mere 10 amp hours of energy before being fully depleted.
Battery manufacturers will often quote the ‘hour rate’ of the battery over the 100 hour test period in order to beef up it’s supposed capacity rating. You may also be given the 20 hour test rate along with other shorter rates like 6 or 8 hours.
Make sure you are aware of these differences before you buy your battery so you know exactly what to expect from your purchase. A combination of misleading DOD information, amp hour rating times and the Peukert effect could result in your battery having much less potential than you bargained for.
Batteries also have a tendency to become less efficient as they age.
Should I Buy a Conventional Flooded ‘Wet’, Gel or AGM Battery ?
Flooded or wet batteries are generally the most commonly used and the cheapest. Filled with sulphuric acid and distilled water they come in two types, serviceable and maintenance free.
Serviceable wet batteries generally require a small level of maintenance and need to be ‘topped up’ periodically in order to replenish fluid losses from the venting of gasses from the electrolyte (battery acid) surrounding the cells. Care has to be taken when handling flooded batteries due to the corrosive nature of their contents and the fact that they are not sealed for maintenance purposes. They also require a cool down period of an hour or so after they have been recharged.
You can accurately check the state of charge of a serviceable wet battery by checking the specific ‘gravity’ of the electrolyte using a hydrometer.
Using a Hydrometer
Maintenance free wet batteries are totally sealed and are not user maintainable. Once the electrolyte solution drops below a certain level or becomes contaminated with eroded sediment from the battery’s lead plates, the battery has to be replaced.
Gel and AGM batteries are both types of valve regulated lead acid batteries (VRLA’s). These are sealed and pressurised but regulated through means of pressure safety valve incase of excess gas build up. Most of the oxygen and hydrogen created during the battery’s charging process is recombined into water preventing evaporation and water loss.
The recombination process is extremely efficient meaning VRLA’s never need to be topped up and gaseous emissions are kept to an absolute minimum.
Instead of sulphuric acid and distilled water, gel batteries are filled with a gelled electrolyte consisting of sulphuric acid and fumed silica. This immobilises the contents and means the battery is safe to mount in almost any position. The gel also provides the battery with greater durability, shock resistance and makes them immune to leaks and cracks. They also have a much higher power to weight ratio that wet batteries.
AGM absorbed glass mat batteries are comprised of an electrolyte absorbed in a sponge like mat of glass fibres. Their construction makes them even better performers than gel batteries. AGM technology is the the newest and most effective form of battery construction and as expected is the most expensive.
Gel and AGM VRLA batteries also self discharge at a much lower rate when in storage and have a higher charging efficiency than flooded batteries. This means they need less power to charge, and they stay charged for much longer when not in use.
If you want a battery to last as long as possible, you need to buy a quality multi stage or ‘intelligent’ charger capable of dealing with your battery’s requirements. Over charging a battery, or charging it too fast, to slow, or at the wrong current will seriously affect it’s future capacity to store and deliver charge. Cheap chargers are not a good investment.
You should choose a charger according to the job it is required for. Wet batteries and VRLA’s charge at different rates so ensure the charger you buy is capable of supplying your batteries needs.
To buy the correct rated charger you should think about the time constraints at which you operate.
If you need a charger capable of recharging your batteries over short periods of time and on a daily basis, you will need one with a high current rating. If you are only using them every once in a while then you could get away with a cheaper, smaller rated charger which would do the job over longer time period.
e.g If a 100 Ah battery needs a power input of around 110 Ah to fully charge it, then a 10 Ah charger will take approximately 11 hours to do the job. A 25 Ah charger should only take around 4.5 hours.
You must also consider the physical conditions your charger will be working under. If your set up is subjected to wet or damp environments or exposed to the elements then a waterproof charger may be necessary.
Ensure your charger has at least 3 charging stages.
1. Bulk stage – For the bulk of the main charging capacity.
2. Absorption stage – Tapering current for the last 10-20% of charge.
3. Float stage – Maintains a very low charge in periods of storage to prevent battery discharge.
Battery Care and Storage
Even an expensive marine or deep cycle battery won’t last long if you don’t look after it properly. This includes charging it correctly and with the right equipment, keeping up the maintenance and correct storage at times when it is not in use.
Marine and deep cycle batteries should be charged with a lower current and over a longer period of time than a regular starter battery.
Always use a multi stage charger. This will extend the life of your batteries. Using an average car starter battery charger to charge your deep cycle batteries will shorten their life span. If you only have a 1 or 2 stage charger, ensure the battery is disconnected once it is fully charged. Overcharging a battery will also seriously affect its long term capacity.
A deep cycle battery should never be discharged to below 20% of its initial capacity and it’s voltage should not be allowed to drop below it’s rated voltage.
In storage, a battery will slowly discharge by itself and over a prolonged period of time if not maintained, will completely exhaust it’s charge. This can cause irreparable damage to the cells.
It is important to check the charge levels of your battery every month or two. Recharge your battery on a slow trickle charge if it needs a top up.
Batteries should never be stored in very cold or freezing conditions as this can cause irreparable damage to cells and casing. Always store your battery in cool dry conditions away from the elements, especially in winter and over long periods of inactivity.
A battery should always be stored in a fully charged state. Doing this will also help prevent it from freezing if it does encounter cold conditions.
Do not store in hot environments as this increases the rate at which they self discharge. They should never be exposed to direct heat from heaters and radiators etc.
All batteries should be stored in well ventilated areas. Wet, sealed and gel batteries contain sulphuric acid and lead. These substances are toxic and can give off poisonous fumes.
Charge your wet batteries in well ventilated areas. A charging battery gives off hydrogen gas which is flammable and explosive.
Now you know a bit more about batteries, take a look at my other guides on how to use them to power your equipment outdoors.
For time and legal reasons I don’t answer reader’s questions on calculations or individual set up’s, but if you need to know anything about creating your own power set up or need advice on calculations, make sure you fully read through my battery guide and posts on inverters, battery calculations and battery connections.
There you should find all you need to know to help you get started.
Other Posts of Interest