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| Mobility Batteries:
Technology and Maintenance as seen in Home Health Products, January 2003 by Gale Kimbrough
With the steady increase of mobility freedom, the term total mobility has become commonplace in the Home Health Care wheelchair/scooter market. Wheeled medical carts of all kinds have emerged lately with improved mobility capabilities. Due to their improved mobility, people have choices of going places that they could not have imagined just a few years ago. One of the contributing factors to this change has been the number, type and capacity of batteries available to power the units and accommodate this freedom of movement. Sealed lead-acid batteries have become the heart of this mobility freedom. They are powerful, compact and maintenance-free. |
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| MOBILITY BATTERY TECHNOLOGY | ||||||||||||||||||
| Gel versus AGM | ||||||||||||||||||
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There are two types of sealed lead-acid batteries in this market: AGM (Absorbed Glass Mat) and Gel. Both types are considered maintenance-free, which means they require no water addition and can be mounted in nearly any position. AGM and Gel both use lead plates, VRLA (Valve Regulated Lead Acid) technology and recombinant chemistries, but that's where the similarities stop.
Most Gel batteries have lead plates with traditional leaf separators. The primary distinction comes from silicates being added to the liquid electrolyte allowing the electrolyte to become gelled and to form fissures in the gelled electrolyte that permit the chemical recombination process to take place during discharge and recharge. The AGM, as its name indicates, is a product that uses a process where the lead plates have a separator made from a highly absorbent material, permitting virtually 100% of the electrolyte to be captivated and soaked into this separator material and allowing the recombination chemical process to occur during discharge and recharge. Today's AGM technology has a dramatically improved cycle life and often offers a lower cost per cycle for the customer. Both battery manufacturing technologies have been around for more than 20 years. Both are acceptable for unrestricted travel and meet U.S. nonspillable restrictions. For many years, the Gel battery was only used in the deep-cycle market and the AGM battery was used for an immediate high-output-current requirement only. The AGM was considered a good starting type battery but suffered from lack of sufficient deep cycles. However, AGM technology has dramatically improved in the last few years, particularly the increase of the deep cycles that can be produced. In fact, some DCS (Deep Cycle Series) AGM batteries now nearly double the cycle life of Gel batteries. And the Gel battery normally takes 10-20 cycles of use before it starts to perform to its rated capacity whereas the AGM reaches 95-100% capacity from the start. Battery Cycles A cycle is one discharge and one recharge of a battery. If the battery is used for four hours or eight hours before being returned to recharge, each case is considered one cycle. The difference between the two cycles is the depth of discharge. Example: A cart has two 33aH batteries connected in parallel with a discharge level of five amps. The depth of discharge (DOD) for four hours at a five-amp discharge is approximately 30%, whereas eight hours at a five-amp discharge is an estimated 60%. The batteries should be able to perform approximately 800 cycles at 60% DOD (according to actual test data) while the number of cycles would more than double to an estimated 1,800 cycles at only 30% DOD. The deeper the discharge, the lower the total amount of cycles. If the normal DOD is 30% (70% state of charge) on a normal day's use, that could result in 1,800 cycles or many years of use. Power versus Run Time Power is mistaken sometimes for operating time or run time. Run time is extremely important to the user, who doesn't want to run out at the wrong place or time. When selecting batteries for the best aH rating, make sure that you are comparing like ratings; be wary of misleading numbers that are based on different discharge rates. Example: A 29aH battery, based on a five-hour discharge rate, offers additional run time compared to one rated at 26.5aH at the same five-hour discharge rate. If a battery is tested at a 20-hour rate, the same 29aH battery is rated now at 33aH while the 26.5aH is rated at 31aH. |
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| MOBILITY BATTERY CARE & MAINTENANCE | ||||||||||||||||||
| Visual Inspection | ||||||||||||||||||
| Even though AGM and Gel type batteries are considered maintenance-free, you may help extend your battery life by performing a quick visual inspection of the battery and related connections. If the battery run time seems to be diminishing, first check to ensure that the charger is operating correctly. Second, check the battery connections. Loose terminal connections can add resistance to the charge input and result in low charge to the batteries. Third, check battery temperature during the charging process. If a battery is hot-to-the-touch, immediately disconnect charger and have batteries tested. And fourth, make sure that batteries are secured properly. Even though both AGM and Gel batteries are highly resistant to vibration and impact, battery life will be affected if they are not properly secured.
Preconditioning You do not need to discharge new batteries to extreme levels. Battery users are commonly and incorrectly told to discharge their battery to a 10-20% depth of discharge the first 10 or 15 cycles. Or they may receive advice to deeply discharge their battery the first 5-10 cycles to allow a deep-cycle battery to "find its capacity level." The truth is that sealed lead-acid batteries do not retain any memory and therefore do not need to find their capacity level. They come to the customer ready to be used from day one. You do not need to baby new batteries when it comes to discharging. Despite faulty information to the contrary, sealed lead-acid batteries, especially AGM, come to the dealer at virtually 100% capacity. They are therefore ready to be used and require no preconditioning. Some Gel manufacturers suggest an initial conditioning time before the battery is discharged to normal levels; they say that for the first 5-10 cycles the battery should not to be deeply discharged. The AGM battery does not require that type of special care or consideration. Opportunity Charging The customer should plug the chair to the charger after using it each day. This will help extend the life of the battery. The battery does not need to be discharged to a specific level before recharging. When batteries are allowed to discharge to a deeper depth of discharge level like 50%, the amount of total cycle life will be about half that of a battery that is cycled down to only 30% DOD. It is always important to recharge batteries as close to 100% as possible immediately after use. A battery that sits used and uncharged for long periods of time is less likely to offer long service life. Battery Replacement Replace all batteries at once. When one battery within a group of batteries is determined to be bad, should you replace them all? Normally you should replace the set, but it depends on the batteries' age and number of cycles. If one battery in a set is less than six months old and determined to be bad, typically the one bad battery can be replaced without causing a problem to the set. If the battery is more than one year old and the average DOD is 60%, then the cycle life may be half used up. Placing a new battery into a set with a battery like this can result in reduced service life of the newly installed battery. However, if the one-year-old batteries have been used (cycled) minimally and recharged properly, it may be fine to install a new battery in parallel with the other good batteries. It is even more critical to replace both batteries if they are connected in series (two 12-volt batteries connected for a 24-volt scooter/chair). Batteries connected in series will only allow the amount of amps available in the weakest cell. If one battery has a weak or bad cell and a new battery is placed in series with that battery, it will not perform any stronger than the weakest. Also, it is recommended that the 24-volt system be tested and replaced by a professional. Select a battery supplier that enables you to replace batteries anywhere. With increased mobility of the home health care market, it is becoming more and more important that the customer has access to batteries anywhere across the land. Deal with a supplier or dealer that has nationwide capabilities for supplying batteries and service. To help your customers with their mobility battery purchases, be sure that you have the most current information on AGM and Gel technologies to help them understand the similarities and differences. Offer them maintenance tips for extending their battery life, and help dispel the common battery-maintenance tips, such as the need to precondition new batteries. Freedom in mobility is what your customers want most, and you can offer them the battery knowledge that will help them maximize their freedom. |
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