Recipe for manual battery charging

Two thoughts / your decision. Money for wasted gasoline, or slight reduction in battery lifespan. Choose one. It takes thirty three gallons of gasoline to purchase your battery.

At 20C I insert enough amperage to raise the voltage to 14.8 but no higher. Throttling the voltage is not easy, but do the best you can. With a standard TRANSFORMER TYPE battery charger you can connect the battery charger AC lead through a VARIAC and then twist the dial on the variac to whatever you want. With a group 27 cyclable battery you should be seeing 42+ amperes.

At 14.8 volts at 20C when the electrolyte starts to bubble more than two bubbles per second per cell, I'll back the voltage down to 14.4. It'll stay there for an hour and a half or so. Again I manage to struggle out of my easy chair and peer into the cells with a flashlight. Same recipe for bubbling. The amperage will have spanned from around 38 to mid to high twenties. Let the damned thing CHARGE until you can count those bubbles. This is where manual charging kicks-butt as far as time is concerned.

Feel the battery case. A whole side. If one or all areas feel warm, say thirty degrees above ambient but LESS than 50C or 122F, stop the charging. The voltage will start to rise if you do not twist the dial on the VARIAC down. Let the voltage rise to 14.8 again. Amperage should now be in the teens.

Voltage limited charging will reduce the lifespan of the battery perhaps ten percent over an absolutely perfectly "recommended show charged" battery that sees the same kWh transaction.

Those extremely expensive smart chargers with all the bells and whistles are doing a -better- job than they used to, but as far as plug in and forget for regularly cycled off grid (boondock) camping. The manual method listed above will save about 30% of the time and actually get the battery to 100% full specific gravity. Chargers that are connected mostly to the grid and batteries that do not see regular and prolonged deep cycling make this black and white with various shades of gray.

Paying sixteen dollars and thirty cents for 5 gallons of gasoline on the other hand makes me see everything -red-

How many gallons of fuel equals a battery..............not enough...

^^^ you are fine as that is an automatic charger.
OP was asking about a manual charger.... when to call it done.

I guess I am wondering what I am doing wrong then. I have two 120AH AGM deep cycle batteries in parallel and I use a Scheumacher battery charger http://www.batterystuff.com/battery-chargers/6-volt/PSC-12500A(DSR).html. I just hook it up and plug it in, set the proper settings on it and let it go to town. When the green light comes on, I unplug it. Am I doing something bad to my batteries?

Time in absorption should be 1.5x the time it takes to reach 14.6/14.8 zone during bulk charge. Then float.
Or hold 14.6/14.8 until amps drop to .5% of capacity. 100Ah = .5 amps
That is my recipe for charging a battery with no load.

Yes the amps taper with a fully manual charger, at least everyone I have seen. :)

Will amps taper with a fully manual charger? I'm just trying to understand how a fully manual charge would be conducted. It's more for knowledge than anything.

MEX just mentioned this recently but I don't remember the exact post. It's not until voltage rises to a certain point but when amps taper to a certain percentage of total capacity. I don't remember the percentage. Search MEX's recent posts.

You can just follow the established rules for charging deep cycle batteries.

Consider this brochure report from Progressive dynamics
"Progressive Dynamics ran this test on the amount of time it took a PD9155 (55-amp) converter/charger set to three different output voltages to recharge a 125 AH (Amp Hour) battery after it was fully discharged to 10.5-volts.

14.4-VOLTS (Boost Mode) – Returned the battery to 90% of full charge in approximately 3-hours. The battery reached full charge in approximately 11 hours.

13.6-VOLTS (Normal Mode) – Required 40-hours to return the battery to 90% of full charge and 78-hours to reach full charge.

13.2-VOLTS (Storage Mode) – Required 60-hours to return the battery to 90% of full charge and 100-hours to reach full charge."

If you want to recharge your battery in three hours time that has been discharged to around 40-50% charge state, start out with 14.4VDC output from your portable charger. Run this for two hours... Then change the portable charger to 13.6VDC output and charge for an additional ONE hour.

Your battery should now be at 90% SOC and can be used right away and give full performance. A quick test would be to let the battery settle down for a few minutes and make a measurement across the battery terminals. It should read 12.5-6VDC

If you want to get a FULL 100% charge state then after the ONE HOUR of 13.6VDC drop the DC voltage down to 13.2VDC and run for an additional 9-10 hours. Then let the battery settle down for a few minutes and you should now read 12.6-7VDC at the terminals.

This is what I would do at any rate if all I had was a portable battery charger.

You are just duplicating what the smart mode chargers do automatically with your manual DC Voltage settings...The batteries being charged will determine how many amps are being drawn. You just have to have around 20AMP of current available to use per battery being charged. i.e My three 85AH Interstate batteries start out drawing around 53 AMPS from my PD9260C converter/charger when I first hit them with 14.4DC. After two hours the current has dropped down to around 8AMPS. When it switches to 13.6VDC charge voltage it drops to around 6AMPS and stays at that level for the additional hour of charging.

This is what I measure at any rate when I am re-charging my three 85AH Interstate batteries in parallel.

Roy Ken