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Among the biggest mobility mysteries to power wheelchair providers and consumers alike is the age-old question, Are my batteries bad?

Of course, there are the obvious signs of deteriorated batteries – reduced range, erratic battery gauge readings, or a dramatic change in charging time.

However, how does one absolutely know the true “condition” of one's batteries, scientifically determining if the batteries are in great shape, mid-life, or in need of immediate replacement?

Through proper testing, that's how.

Starting With What Not to Do
When it comes to battery testing, too many providers and consumers mistakenly focus on testing the batteries' “state-of-charge,” not the batteries' actual “state-of-health.” For example, placing a volt meter on the static system simply tells you the batteries' state-of-charge – which is exactly what the power wheelchair's battery gauge does. What's more, there's a recent generation of digital “battery testers” that claim to read a battery's state-of-charge, as well as its state-of health within 15 seconds. While these “testers” can suggest that there's a bad cell or some level of sulfation, they're not an entirely accurate way to tell the true “state-of-health” of the battery – that is, they can't tell you with absolute certainty whether a battery is in perfect condition or internally deteriorated, needing replacement, or in a state somewhere in-between.

Time is Everything
A red flag for an improper battery test is when it's all but instantaneous. Again, a volt meter or a 15-second test truly can't tell the entirety of a battery's condition – that is, whether its lifespan is diminished. To the contrary, a true test of a battery's condition takes hours, where a fully charged battery is placed under a load and discharged at a controlled rate – as in, 20A, for example – and its capacity is determined.

How Thorough Battery Testing is Performed
The role of battery testing is to determine the general condition of a battery and its ability to deliver the specified performance compared with a new battery, taking into account such factors as charge acceptance, internal resistance, voltage, and self-discharge.

“Processor controlled capacity testers” are among the surest, most foolproof battery testing methods today. Commonly distributed under the brands of Forex and MK, processor controlled capacity testers take a fully charged  battery, and discharge it while collecting internal data that provides a virtually exact number that tells the life left in a battery by percentage. For example, a battery's full capacity is 100% when new, but as it deteriorates during normal usage, its capacity drops incrementally. If a battery retains 80% of its capacity, then it's still a totally viable battery (the battery has some reduced performance – read that, capacity – but not enough to detract from most power wheelchair use. However, if a battery shows as only having 50% capacity, then that's a major deterioration, one that a user would notice – allowing only half of optimal driving range – and the batteries need replacing.

Therefore, a processor controlled capacity tester is among the surest ways to tell whether power wheelchair batteries are good, mid-life, or need replacing. However, such testing does take several hours, so a provider typically keeps the power wheelchair overnight for testing.

Look for the Right Tester
If you ever have concerns toward your power wheelchair's batteries, and your provider wishes to test them, realize that among the most accurate information comes from not a volt meter or an old-fashioned ”load test,” but from a processor controlled capacity tester. And, if your provider has the proper equipment – as he or she should – you'll not only know if your batteries are “good” or “bad,” but, more importantly, you'll know the exact condition of your batteries – that is, how much life they have left, right down to the decimal point.

Published 8/09, Copyright 2009,