Sealed lead acid batteries are fine if you're starting a car. But they have inherent problems, as do other technologies. Over time an SLA battery will simply go dead. These types of batteries are not made for deep discharge, or for sitting on a shelf over the long winter months. Life expectancy can be as little as 200 charge cycles – at best 500 cycles. And the worst thing about it is that you probably won't even know until your light finally just won't light (or the battery boils over during charging).
NiMH and NiCD are a little better, but come with their own set of problems. And they all take 8 to 10 hours to recharge!
This chart compares the brightness (actual watts, over 8 hour time period) of an 11 watt lamp powered by a 7 pound, 8AH lead-acid battery to a lamp powered by a set of two 4.6AH (9.2AH total) UV-PowerPak batteries (total weight of less than 3 lbs).
What is Cell Balancing?
12V battery packs are made by "stringing together" lower voltage individual batteries. A typical individual battery cell generates around two volts (on average). If you wire 6 of these cells in series you will get 12vdc (lead-acid for example). Some cells may generate only 1.2v, thus 10 cells are needed to get 12vdc (NiMH). Others may generate slightly more voltage, but the principal remains the same. Simply wire in series the number of batteries needed to get 12vdc.
Because of production tolerances, uneven temperature distribution and differences in the ageing characteristics of particular cells it is possible that individual cells in a series chain could become overstressed leading to premature failure of the cell. During the charging cycle, if there is a degraded cell in the chain with a diminished capacity, there is a danger that once it has reached its full charge it will be subject to overcharging until the rest of the cells in the chain reach their full charge. The result is temperature and pressure build up and possible damage to the cell. During discharging, it is even possible for the voltage on the weaker cells to be reversed as they become fully discharged before the rest of the cells resulting in (permanent) failure of the cell.
Because Lead acid and NiMH cells can withstand a level of over-voltage without sustaining permanent damage, a degree of cell balancing or charge equalization can occur naturally with these technologies simply by prolonging the charging time since the fully charged cells will release energy by gassing (getting hot) until the weaker cells reach their full charge. Usually this is not harmful to these cells unless the imbalance is severe – then heat can permanently damage a cell, or worse – cause a fire. Although the problem is reduced with Lead acid, NiMH batteries and some other cell chemistries, it is not completely eliminated and solutions should be used for most multicell applications. Heat is a battery's enemy so we must do everything to limit this heat, but insure maximum charge.
Lithium cells cannot tolerate over-charging. The cells in the LiFE packs are Lithium Ion and thus need some kind of balancing to prevent this from happening. This is taken care of automatically during the charge process by the battery charger (such as a Hyperion Charger and LBA10 Cell Balancer). At the end of a charge each cell in the battery pack will be charged to its optimum voltage, ready for an evening's use.
A side benefit to this balancing procedure is MAXIMUM POWER (all cells are fully charged, doing their job) and longer life from your battery pack – both in charge times, and in simple longevity. A lead-acid battery with a discharged cell - at a minimum - will provide less runtime, and can risk cell reversal and ultimate failure of the entire battery. NiMH packs can heat up to a point where they might even catch fire if not protected by an over temperature sensor during charging. Intelligent charging and safe battery technology solves this problem and is recommended for all multi-cell applications – and is required for Lithium Battery Packs.
*****Important Note on the Use of LiFE*****
Do not allow your LiFE battery pack to discharge below 12VDC. IF the voltage drops below this point it could cause problems in recharging them (you might have to juice them up a little in NiMH mode before you can charge them properly in A123 mode). Even worse, discharging below 11VDC could permanently ruin one (or more) of the cells. Use the battery monitor and watch it while using your lamp. Switch packs immediately when your pack drops to 12VDC (or before). Once one of these packs starts to drop you only have a few minutes (15 to 30) to change packs out.
Hyperion Battery Charger - ideal for charging LiFE and NiMH battery packs
12vdc cigarette lighter to Anderson Powerpole Adaptor
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