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10 Key Points To Consider When Sourcing A Custom Manufactured Battery Pack

Posted on 18th July 2013

Selecting the right battery technology, in the right size and at the right cost, can be difficult. Here are some pointers to help make the decision that bit easier.

What’s the best way to get impartial advice?
Look for a battery supplier who is not tied to a single manufacturer or technology. Being guided toward a product which does not fully meet the cycle life or temperature range requirements of an application, for example, can lead to project failure. Always keep an open mind.

Are rechargeable batteries cost effective?
Primary non-rechargeable batteries are still the best choice for many applications. All batteries inherently suffer from self-discharge and this tends to be far higher in rechargeable batteries.  Therefore, unless you plan to provide a means of regular recharge, it is almost certainly better to specify a primary battery.

Will battery performance levels always be supplied?
You can expect this on a new battery, although figures are often related to single cell tests under strict ISO test conditions; if you challenge the performance, this must be considered. Chemical changes within the cell will also affect performance with age.  Manufacturers will normally state an end of life figure of between 60 and 80 per cent of the original battery capacity after a given number of cycles. When choosing a battery, this end of life figure needs to be carefully considered.

Are all battery sizes standard?
All cylindrical cells are made to defined sizes and are generally interchangeable, however many cells exist outside of these standard sizes. For example, if you look at the range of lithium polymer cells offered by some manufacturers, there seems to be one for every application. If you try to order a few thousand you will likely  be disappointed, yet if you need a few million, they will become available. However, don’t get caught out with a single sourced cell or battery - you can guarantee this was developed for a large application and the cell will be withdrawn at the end of the product life, leaving you with a problem.

Is Lithium Battery Technology Always The Right Solution?
At present, lithium technologies provide the greatest energy density, but in static or even portable applications where weight is not the first priority, other technologies such as valve regulated lead acid or Ni-MH are still often a better and cheaper solution. Sometimes lithium isn’t right because of environmental or life cycle considerations.

Are lithium batteries safe to use?
Generally, the answer is yes. The key to producing a safe battery is to build in several levels of protection to maintain it within safe limits. This is likely to include an electronic protection circuit to prevent over charge, over discharge and over current, a thermistor and thermostat or thermal fuse and a resettable fuse. Consideration has to be given to the battery pack build to prevent mutual heating of cells and to the end product to fully ensure there are no hot-spots located close to the battery, which may cause cells to become imbalanced.

Do new lithium battery packs require any testing?
After prototyping, new lithium battery designs must be tested to strict limits described in UN38.3. There is  a cost for this, so if this doesn’t fit your project budget, you’re probably choosing the wrong battery technology.

Is a lithium battery viable for a small scale project?
To avoid costly testing, it’s often possible to pick a standard lithium battery that already carries UN38.3 approval. Try to avoid strange shapes and voltages, find out what’s available and plan around it. If volumes increase, choosing a bespoke design may become an option, perhaps improving capacity at the same time.

Is battery recycling compulsory?
No, it isn’t compulsory, but legislation is in place to increase the overall levels of recycling.  With the introduction of the batteries directive 2006/66/EC in 2006, European governments were charged with laying out their own country's specific legislation. At the same time, it also made battery producers responsible for the cost of recycling.  In the UK, this directive was transcribed into law as The Batteries and Accumulators (Placing on the Market) Regulations 2008 and the Waste Batteries and Accumulators Regulations 2009. The first deals with identifying batteries as separate waste and the second with laying out a recycling framework. Battery producers must register for compliance and provide a route for take-back of batteries, either through a compliance scheme or direct. They also must provide details of all the batteries they have placed on the market in a given year. All battery producers, including pack builders, must state their producer registration number on their paperwork so always ask your supplier for their registration number.

Where are batteries heading?
At present the emphasis is on incrementally increasing the energy density of Li-Ion and lithium polymer and providing safer lower energy density.  Lithium alternatives such as lithium iron phosphate (LiFeP04) offer this. These technologies offer other benefits such as high cycle life and better high and low temperature performance.

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