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Batteries - Keeping things in perspective

(Revised October 2004)

In recent years, batteries seem to have taken on a new perspective, as a result of more and more electrical equipment becoming the norm. For example, typical loads on A & E ambulances, ‘on a shout’, can be in excess of a 100amps, thereby placing considerably more emphasis on the amount of available battery capacity, or reservoir.

Marine craft, motorhomes and other specialised vehicles are now using inverters to power A.C. equipment. This can have a devastating effect on batteries if there is insufficient capacity and an inadequate state-of-charge.

A common perception is that battery make or type has a considerable bearing on the equation. We are now familiar with terms such as: traction and semi-traction, deep-cycle, leisure, nickel-cadmium, pure lead, alkaline, gel, spiral cell technology, gas recombination techniques, VRLA, maintenance-free, hybrid construction, double separators, C/20, CCA, reserve capacity, A.Hrs. etc., all of which can be bewildering to the uninitiated.

There are few ‘bad’ batteries, in this day and age, but, arguably, there are ‘fashions’. The question arises, though, ‘Which battery should I use’?

Deep-cycle, Cyclic and Leisure batteries are common terms used in trying to deal with insufficient capacity. By ‘inhibiting’ the current demand from a battery, it is possible to allow higher levels of discharge, especially if the plates are thicker, with a higher lead content.

If batteries are properly charged in the first instance i.e. to 100% s.o.c., there is less need to take the batteries below 50% s.o.c. Virtually all batteries suffer some kind of damage if they do go below this figure, deep-cycle included. This 50% s.o.c. notion is a very important consideration, therefore, and should be taken into account when contemplating the design of a battery related system. First establish the total consumption in A.Hrs., then double the figure to give the necessary battery capacity, basically.

As with most things, everything comes down to choice and what you want to pay. Our view is that heavy-duty truck batteries provide the best compromise in terms of capacity, performance, price and are therefore good value for money.

In a typical supermarket multi-drop scenario, for example, the vehicle tail-lift intermittently draws approximately 100amps at 24volts for around an hour. The batteries then have to be capable of starting a vehicle and repeat the performance, say an hour or two later. It is reasonable to suppose that if these batteries can handle this sort of treatment, they should be able to keep abreast of e.g. narrowboat or yacht requirements.

Typical common types available are:

Provided these batteries are not allowed to fall below 50% s.o.c. (12.2volts), regularly, you will get good performance and reasonable life. Semi-traction batteries are a little more expensive but excellent value for money, having superior cyclical performance.

High tech. batteries are gaining ground in the popularity stakes, especially with increasing focus on Health & Safety and the possible affects of accidents in both marine and automotive situations.

Water loss has been reduced considerably and, in some cases, eliminated totally, by the replacement of antimony in the battery grids by calcium, making sealed batteries possible, reducing maintenance and preventing noxious fumes.

The scope of GEL batteries has widened, also, so that, in addition to originally being used as back-up support for computers, emergency lighting and security alarms, etc., being totally sealed with low self-discharge, they can start engines, be deep-cycled and still operate under water, if necessary.

GEL batteries can be mounted in a variety of positions. They have a long service life, at least twice that of ‘wet’ batteries, and are maintenance-free, so the higher cost becomes less of an issue, especially with the added benefits of increased safety.

VRLA batteries, employing spiral cell or orbital grid technology with gas recombination, fall into a similar category to gel. These batteries have a high cranking capability and, because of the low internal resistance of the plates, recharging is quicker than for conventional wet batteries and service life is three times higher.

These batteries are expensive and are limited in terms of capacity, but the advantages are evident when starting is vitally important and where vehicle damage could become an issue if wet batteries were used. This type readily lends itself to police and ambulance applications, but less so in a marine environment because of their capacity limitations, unless you have deep pockets!

AGM (Absorbed Glass Mat) are presently ‘flavour of the month’. Similar to gel, the manufacturers claims are amazing: greater life and cyclability, low self-discharge, ability to remain in a discharged condition for long periods without damage. The biggest claim is that they can be replenished at an extraordinarily high charging rate, the implication being that only half the calculated battery capacity is therefore required.

Our own tests have shown that AGM are good batteries, though these claims are somewhat exaggerated. In addition, we would not recommend the high re-charge regime suggested.

In the leisure field, e.g. yachts, motorhomes, caravans and inland waterways craft, carbon fibre batteries are popular, because of price and especially a five-year guarantee. Faster charging is also claimed. So far, from our experience and tests, we need more convincing. A five year warranty is no substitute for performance.

Battery variety has never been greater, so there is very much a case of ‘horses for courses’.

ADVERC are presently conducting a performance survey, covering a wide range of battery types and technology, which may be published sometime next year. In the meantime, we would be pleased to advise you on the best approach for particular applications. The correct battery, accompanied by an ADVERC Battery Management System, is a fundamental step for a ‘fit and forget’ solution to battery related problems and issues.

If you need to know more, or cannot find what you are looking for on this website, please contact us.

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