Need to make charge indicator for 4 V 1 Ah Lead Acid battery

I have made a solar study lamp. I am using 4 volts 1 Ah lead acid battery for the same and 3 Watt solar panel. It charges well with the current circuit. But it does not have a charge indicator. I am looking for a battery charging circuit with charge indicators as follows:

1. Low battery indicator 
2. Battery full indicator
3. Charging indicator - to indicate battery is getting charged

Trying to keep this simple and inexpensive as this lamp is a part of social initiative for rural areas.

Thanks in advance! 

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Manoj BR1 year ago

I to have a 4 volts 1ah battery it charges arround 5v 100mah - 300mah . To make charge indicator for this you can make use of zeener diodes of 4.7 volts for charging indicator and 3.7 volts for middle stage indication . We can make use of led's for visual indication. For fully charged 4v battery the voltage will be 4.6-4.7volts . Hence for fully charged battery the charging led will be on even after charger is unpluged. try the below circuit once on bread board .

R1,R2 &R3 are 330 ohms resistor

Led1 is green

Led2 is orange

Led3 is red

ZD1 is 1N4728 ( 3.3V)

ZD2 is 1N4732(4.7V)

All the 3 wiil be on if the battery is fully charged or charging(when charger is connected).

If 2 led's are on the battery is in middle stage.

when 1 led(red) is on then it will be low charge state. You can add still more stages by adding zeener diodes of 3.7v 4.3 v . Just reverse bias the zd and forward bias the led of color of your choice next to it.

Screenshot_2016-03-20-08-41-20 (1).png

LA batteries are pretty easy to keep tabs on, all you need is someway of monitoring the cell voltage

The excellent Wikipedia entry on Lead Acid batteries has all you need.

Don't charge the battery fast, don't empty it, and don't keep charging it and it will last a very long time.

Voltages for common usages

For the three-stage charging procedure of lead acid batteries, see IUoU battery charging.

These are general voltage ranges per cell:

  • Open-circuit (quiescent) at full charge: 2.10 V
  • Open-circuit at full discharge: 1.95 V
  • Loaded at full discharge: 1.75 V
  • Continuous-preservation (float) charging: 2.23 V for gelled
    electrolyte; 2.25 V for AGM (absorbed glass mat) and 2.32 V for flooded
  1. All voltages are at 20 °C (68 °F), and must be adjusted for
    temperature changes. The open-circuit voltage cannot be adjusted with a
    simple temperature coefficient because it is non-linear (coefficient
    varies with temperature). See voltage vs. temperature table.
  2. Float voltage recommendations vary among manufacturers due to different lead acid concentration and positive plate grid alloy.
  3. Precise float voltage (±0.05 V) is critical to longevity; insufficient voltage (causes sulfation) is almost as detrimental as excessive voltage (causes positive plate corrosion, expansion and electrolyte loss.)

Typical (daily) charging: 2.37–2.4 V (depending on temperature and manufacturer's recommendation)

  • Equalization charging (for flooded lead acids): 2.5–2.67[13] V (5A per 100Ah,[14] Battery temperature must be absolutely monitored very closely, check manufacturers recommendation)
  • Charging in sulfated state (stored discharged for days or weeks) not accepting small charge current: > 3 V[15] (only until a charge current is flowing)
  • Charging in sulfated state: up to 2.6[16]–2.66 V [16]
  • Discharging in sulfated state: 1.6 V (when charging at low rates doesn't improve, discharge rate approximately 5A per 10Ah)[16]
  • Gassing threshold: 2.415[17]–2.48[18] V for sealed, 2.41 V for PzS, 2.36–2.41 V for GiS, PzV, GiV[19] (the value is manufacturer specific, gas is always produced even in storage,[20]
    99% of the gas production recombines under normal charging conditions,
    the higher the voltage exponentially more gas is produced: from 2.3 to
    2.5 is factor 1 to > 20,[21] charging above the gassing voltage with high charging current the side reaction will occur enhanced[19])
rahuldj (author) 1 year ago

Thank you all for your help, I will check details all of you have provided.

Manoj BR1 year ago

Sorry for the wrong circuit below.

rickharris1 year ago

Where will you get a 4 volt lead acid battery from?

A single lead acid cell fully charged will be around 2.3 volts and perhaps 4 volts for 2 cells. BUT as far as I know you can't get a 2 cell lead acid battery.


You may wonder why so often we just give a google URL for questions like this but the honest reason is why reinvent the wheel when the information is already there or mostely there.

You can get 4V ones, I had a few back in the day.
In my case they were used as long term backup systems for electronics to keep the data alive where no EEPROM or simial is available.
Some camping lanterns used them as well.

:-) nothing like minaturisation!

People like Hawker sell the "Cyclon" lead acid cells in 2V multiples. Cyclon cells are amazing.

Never seen them. Only seen Nife cells as singles.