How do I charge lead-acid batteries?

I have two 6-volt ~4.5 AH batteries, and I'm not sure how to charge them. I know that overcharging and voltage regulation can be an issue. They have markings on the outside that say "standby voltage ( voltage)", "intermettent use voltage (voltage)", and I was wondering what voltage I use to charge them, how I know when they're fully charged, etc. Advice is welcome. Thanks!

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the re-design guy said it closer to right the general rule for lead acid battery's is to charge 3volts over batteries rating as in if it's a 6v charge with 9 and 12 with 14.5-15v. and to monitor its voltage as its charging once the batteries rated voltage is met "stop the charge". a totally dead battery should be trickle charged "less than 600-800mA" until the charging current is less than batteries rated charging current or until battery shows a voltage 2/3 of its rating this prevents boiling of internal liquids which usually ends in rupture of batteries or flammable vapor.. some batteries show a "max charging current" or a visit to a manufactures website can tell you. think of it like tug-o-war only pushing instead, if 12 guy's push evenly the same from both sides then motion stops. though if you put 3 more on one team than the other, it is upto the ref to stop the game before a crash.. as the battery reaches full its resistance rises and the charging current through the batt stops, the voltage drop is zero"chargers output" then instead of reading the batteries 12v you will begin to see the chargers 14 instead.
chuckr447 months ago

Read this first:

then read this for tables of charging voltages:

ReCreate8 years ago
Just apply 6V of electricity(remember the polarity) for a few hours or overnight. Lead acid batteries tolerate overcharging more than any other battery type.
seandogue8 years ago
Here's a link to teach you a bit more about how lead-acid chemistry batteries should be charged, in case you're a DIY type who wants more than and off-the-shelf solution and has some ability with design and implementation.

If you have access to an adjustable power supply, a quick and dirty method is as follows: Set the output voltage to 7.0 VDC. Monitor the current draw using an Ammeter ( Under $10 multimeter, set for current measurement) until the draw is less than ~100mA. Then set the output to 6.5VDC until the draw is ~10-20mA or less. disconnect the battery and store in a cool dry area. Periodically (every month) connect the battery as noted in the second stage to offset natural self-discharge. You might want to implement some current limiting between the power supply and the battery pack to prevent damage to the supply in the event that the batteries are fully discharged as they will pull considerable current (a freshly discharged lead acid cell looks like a low resistance load)...Read the link I provided...
Re-design8 years ago
Here's the charger you need!
Re-design8 years ago
I used to use 2 - 12 v. 7.1 aH batteries similar to these when I flew RC. I had a special charger that monitored the batteries and turned off when they were charged. It charged them at about 14v. of something like that. I spent about $75 for the charger but it would do lots of other things and charge almost all of the batteries I had.