Because the battery may get overcharged in service. But I've had a number of cars over the years that had "regular" batteries (non maintenance free). The batteries rarely needed water - maybe once or twice a year - and were never even close to a pint down. I have 2 non-maintenance free batteries that were picked up at the side of the road. I've had them for almost a year, and the electrolyte level has not dropped. These batteries are not on a charger, they just sit there. I have another that is on a float charger for 100% of the time, and has been for almost
Some of us refer to such batteries as "maintenance resistant".
With regard to three-stage charging:
I use at Size 31 - 100 AH - gel-cell battery as the main power source for my radio equipment. Gel-cells are REALLY sealed and can be operated in any position. They do not have vent caps, hidden or exposed, and as the name implies, has a gelled electrolyte rather than a liquid electrolyte. Truly maintenance-free discounting the need to check the connections for tightness and corrosian from outside sources.
I recently put a new charger designed for gel-cell charging into service. This is a professional type charger, not an automotive charger (with price to match), and it has a specific setting (dip-switch on control board) for gel-cells. It was recommended as the proper companion to the battery by the local industrial battery supplier.
In addition, if the current drawn by the load while the battery is being charged is greater than 2A (which it is here) a jumper has to be added on the control board to change it to a two-stage charger or else the control circuitry will see the load current as charging current and adjust the voltage upwards to compensate.
I have also found that when in "charge" mode, the DC output has a 60 Hz component which needs to be filtered between the battery-charger junction and the load. One more thing that "they" don't tell you in books or teach in courses.
-- 73 de K2ASP - Phil Kane (Regsitered Professional Electrical Engineer)
I concur with Phil. Gelcells are the true maintenance free battery of choice for a ham shack. I have run my ham shack off 12V gelcell battery banks for at least 25 years. I have always simply floated the battery with a regulated 13.6V 4A power supply. It charges the battery as needed and floats it at 13.6V when the battery becomes charged; no danger of overcharging. If the power goes out, there is no need for switch over . . . shack is still running off the battery. About every 6 or 7 years I replace the battery(s).
More recently I have pulled the AC power supply off in favor of 55watt solar panel with home brew regulator ..... set for 13.6V max. Still works like a dream.
On 08/19/05 12:19 am Ed tossed the following ingredients into the ever-growing pot of cybersoup:
Oops! I got an extra "1" in there for the SG. It should have been 1.175.
Anyway, I did a random series of charging -- sometimes on the 12A setting (although the ammeter never read that high), sometimes on the 2A setting -- and resting cycles, adding water as needed. The SG came up to
1.265 (the bottom of the green on my hydrometer), but the "fully charged" indicator on the charger did not come on.
I then bought a "Vector" 2/6/10A microprocesor-controlled "smart"
3-stage charger (on clearance for a good price) and hooked that up. After a few hours, it showed "FUL"[ly charged], then switched to "FLO"[at]; in the latter mode, it is supposed to monitor the battery voltage (currently 13.8) and "top it up" as needed.
So perhaps this ill-treated battery is not a goner after all.
On 08/16/05 11:24 am Percival P. Cassidy tossed the following ingredients into the ever-growing pot of cybersoup:
At one point the new three-stage charger did indicate "FUL"[l], then switch to "FLO"[at] after I had left the battery on charge for many hours at varying charge rates, but after discharging it again down to
11.2V I couldn't get it to recharge satisfactorily: the charge rate would stay at 10A and the battery would get very warm.
I then realized that the free replacement warranty was good for 18 months rather than 12 and that I still had a few days to go. I took it back to Sam's, and they replaced it free without checking anything other than the date on the receipt. They didn't put it on test in any way and didn't even check the electrolyte level. So now I have a new battery with a new replacement warranty good for 18 months and pro-rated after that.
AND now I know that I'm supposed to check the electrolyte level every month.
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