battery charging voltage

[Boyntonstu]

"Moreover, in order to recharge a battery, the charging source – a battery charger, the vehicle alternator, a solar panel controller – must be at a HIGHER voltage in order to force electrons back into the cells."

Take a battery discharged to 11.9 V and connect it to a 12.8 V constant Voltage source.

The battery will reach its fully charged 12.8 Volts without being connected to a Voltage higher than 12.8.

[Optimistic Paranoid]

"Moreover, in order to recharge a battery, the charging source – a battery charger, the vehicle alternator, a solar panel controller – must be at a HIGHER voltage in order to force electrons back into the cells."

Take a battery discharged to 11.9 V and connect it to a 12.8 V constant Voltage source.

The battery will reach its fully charged 12.8 Volts without being connected to a Voltage higher than 12.8.

In fact, that is NOT what the battery manufacturers say.

The following was lifted from Handy Bob's excellent web site on solar charging:

*VOLTAGE:* For the sake of simplicity, I am only going to talk about the requirements of standard flooded wet cell lead acid batteries, which is what most of us use.  The major points apply to all types of batteries,but the actual numbers will vary.  It is very important for you to research the charging requirements of your batteries if you are using any other type and make sure that your charging system provides what they need, or you could end up damaging them by over charging or never getting them fully charged, which will also damage them.  Battery manufacturer’s specifications say that a standard 12 volt wet cell battery needs to be charged to between 14.4 to 14.8V and then *held there* for some time before it will be fully charged.  The Trojan Battery company says 14.8V daily charge (at 77 degrees F) and Interstate will tell you over 15V.

Trojan’s 2010 Users Guide has a new chart that shows you should actually vary the voltage depending on the amps you supply for charging and even higher voltages are recommended.  Of course they recommend temperature regulation.  So all of those out there who are telling you 14.8V is too high do not know what they are talking about.  How long it takes to get the charge in depends on how far it was discharged.  Trojan says to keep charging until a hydrometer test shows that the battery is charged and not one charger available today can do this.  The best chargers can do a reasonable guess at state of charge by providing constant voltage and watching the amps taper as the battery fills to tell them when the battery is full. 

However, they rely on whatever the designer or programmer gives them for guidelines and are only as good as that data.  Many do no work worth a hoot.  A fully charged battery can be maintained at a full state by applying a 13.2 –13.6 volts “float” charge.  All of the talk about how many amps a charger puts out means nothing.  It is the volts (pressure) that you

need to push the amps (volume) into a battery.  *VOLTS, VOLTS, VOLTS!!*

Also, the amps pushed into a battery at a higher voltage contain more power than those at a lower voltage.  Remember, volts times amps equals watts, so amps pushed at 10% higher volts give you 10% more watts. Therefore, the power stored in the upper range of a battery’s charge is greater, so it is very important to get a full charge.  Low voltage DC is not easy to get through wire without losing power due to voltage drop or resistance.  It is huge problem in an RV.  Use big wires and short wiring runs to get around this.  It is good practice to use one or even two sizes bigger wire than recommended to limit voltage drop.  This charge voltage has to actually reach the battery, not just the output terminals on a charger.  If you cannot get your batteries up to 14.4 volts (14.8 is better & faster) with whatever charging system you have and then keep them there while pushing amps in for more than an hour or two, your batteries will never be full.

*Added in 2014:  *Please realize that the message here is for off grid living, not for being plugged in at an RV park.  A converter that is set lower but left plugged in 24/7 may eventually fill a battery.  It may not, too, but it doesn’t need to be set at 14.8V to work.  Buy a hydrometer if you want to know.

[sternwake]

Perhaps a new Healthy flooded battery dischrged to 11.9v, attached to a charging source limited to 12.8v could fully charge the battery, given enough time like 36+ hours, but no well worked battery is going to get max Specific gravity at such a low voltage.


At 13.6v applied forever on a well cycled is unlikely to max out specific gravity.

Moreover not every battery is 12.8v is full.

My AGM is 13.06v when fully charged andrested, or it was two years ago. It has never rested since.

I get that the original post was designed to promote discussion rather than misinform, but some might not understand that.

The nightly deep cycling of lead acid batteries requires the battery be brought upto absorption voltages for enough time before the next discharge begins. Otherwise the battery is doomed to a premature death.

Those seeking gentle slow recharges when nightly deep cycling have their facts confused

[frater secessus]

The following was lifted from Handy Bob's excellent web site on solar charging:
...
A converter that is set lower but left plugged in 24/7 may eventually fill a battery.  It may not, too, but it doesn’t need to be set at 14.8V to work.  Buy a hydrometer if you want to know.

^ That was at the bottom of the quote, btw.  (not recommending that method)


I would say HandyBob's info is quite good (even if dogmatic/beligerent) but the website and delivery is a clusterfsck.  I tried to summarize his charging puzzle page so that fewer seekers would hang themselves out of frustration.

[Boyntonstu]

With over 300 charge/discharge cycles for my 48.0 V Li-Ion battery using a 48.0 V constant Voltage lab supply, I am 100% confident that it is OK.

Any Voltage above any rechargeable battery that has been discharged will charge the battery to the charger's Voltage.

If a battery is at 12.799 Volts and it is connected to 12.8000 Volts, it will come up to 12.800 Volts.

If you wish to charge it to 13.2 V just connect it to 13.2 V and it will happen.

The electro-chemistry is what makes it work.

"Charging of a lead acid battery can be done in various ways:

Constant Voltage
Constant voltage charging is most commonly used for a sealed lead acid battery. The initial charging current in a constant voltage battery charger is limited by a resistor. "

https://eewiki.net/display/Motley/Charging+Lead+Acid+Battery+Basics

[Cammalu]

Unfortunately when my golf cart was left unplugged for an extended time it would not charge. The batteries were fairly new and when I called the golf cart repair place they told me they would be able to save the batteries by charging on their higher voltage flooder? to get them to charge. I brought it in and it worked. It HAD to have that higher voltage to get them going again.

I know they are doomed to a premature death. I just wanted to point out that there was no way they were going to charge with my regular charger even though it wasn't damaged.

[GotSmart]

"Moreover, in order to recharge a battery, the charging source – a battery charger, the vehicle alternator, a solar panel controller – must be at a HIGHER voltage in order to force electrons back into the cells."

Take a battery discharged to 11.9 V and connect it to a 12.8 V constant Voltage source.

The battery will reach its fully charged 12.8 Volts without being connected to a Voltage higher than 12.8.

Sorry Stu.  Just because you charge it to 12.8 volt does not mean that 12.8 volt is fully charged for that unit.  My system regularly goes beyond 13.6, and the indicator shows it needs more.

Comparing flooded batteries to lithium on charging is intellectually dishonest.  Kind of like using apple juice to write data on lemon juice.

[bLEEp]

I showed 13.7 this AM, I know, impressive. And only about 3/4 full, pre 8 AM, which on the Oregon coast is dim and foggy....


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