Battery maintainer
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Here's the scoop on charging - What we call a battery are simply individual cells in series or parallel to meet specific voltage and current requirements. This is true with lantern batteries, 9 volt batteries, flashlights, radios, etc. ever notice a flashlight dims and flickers with mismatched cells?
Once two batteries are paralleled it's now just one big battery, electrically speaking. It can get expensive for folks who don't get that. There's no way around this. Each individual cell has to be close in voltage or the other cells try to charge it, or vice versa. With conventional lead acid batteries over time there would be one or two cells that needed water and the remedy was long charging to equalize all the cells and get them on the same sheet of music. Equalization is a specific overcharge to around 16 volts to get them all above minimum voltage and specific gravity at after surface charge is removed. With "maintenance free" batteries there is no way to tell other than monitor voltage. And there's no way to add water. Cells must always be charged as a battery, whether series or parallel if you want to realize even the minimum life and advertised performance. Any charger will work, it just takes a while.
Hang a DVM on the battery and monitor the charging voltage. It takes approx. 2 (two) volts above the open circuit voltage before a battery even starts to reach full capacity and starts gassing. This can take several hours. Oftentimes this is the point when people stop charging. While overcharging is possible it takes dedication. Batteries actually "like" to spend extra time on the fully charged side of the scale at 14.5+ and this tends to equalize cell voltage. Smart chargers and maintainers are supposed to do this automatically. Some will automatically switch to float after 5 or 6 hours even if not fully charged. You can "reboot" the charger by unplugging and start the charge cycle again. "Dumb" chargers are usually current limited taper, and if you monitor the voltage rise you can let them reach moderate gassing for several hours and do the same thing. Just don't forget, or put it on a timer.
Once two batteries are paralleled it's now just one big battery, electrically speaking. It can get expensive for folks who don't get that. There's no way around this. Each individual cell has to be close in voltage or the other cells try to charge it, or vice versa. With conventional lead acid batteries over time there would be one or two cells that needed water and the remedy was long charging to equalize all the cells and get them on the same sheet of music. Equalization is a specific overcharge to around 16 volts to get them all above minimum voltage and specific gravity at after surface charge is removed. With "maintenance free" batteries there is no way to tell other than monitor voltage. And there's no way to add water. Cells must always be charged as a battery, whether series or parallel if you want to realize even the minimum life and advertised performance. Any charger will work, it just takes a while.
Hang a DVM on the battery and monitor the charging voltage. It takes approx. 2 (two) volts above the open circuit voltage before a battery even starts to reach full capacity and starts gassing. This can take several hours. Oftentimes this is the point when people stop charging. While overcharging is possible it takes dedication. Batteries actually "like" to spend extra time on the fully charged side of the scale at 14.5+ and this tends to equalize cell voltage. Smart chargers and maintainers are supposed to do this automatically. Some will automatically switch to float after 5 or 6 hours even if not fully charged. You can "reboot" the charger by unplugging and start the charge cycle again. "Dumb" chargers are usually current limited taper, and if you monitor the voltage rise you can let them reach moderate gassing for several hours and do the same thing. Just don't forget, or put it on a timer.
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