Load resistor for 12V battery


I am having Sealed Lead-Acid Rechargeable battery with capacity of 12V / 7.5Ah.

I want to connect a load resistor across the battery for discharging.

The load resistor should be designed in such a way that it should take maximum of 1 Amp current from the battery.

So what is the exact load resistor value and how many watts required for 1 Amp current consumption?

Pls tell me the suggestion.

V = IR

P = IV


You have given only formula.

I need load resistor value that should take 1 Amp current from the battery.

Can you tell us your electronics, programming, arduino, hardware experience?

This is basic Ohms Law.

If you are playing around with SLA batteries, you need to know at least Ohms Law.

What output voltage under load, will you disconnect the load?

Tom.... :slight_smile:

12V / 1A = 12 Ohms

12V X 1 A = 12 Watts

hence 12 Ohms 12 watt resistor; you can use two 12V scooter speedometer dial lamps in parallel or buy 12V 12 watt lamp bulb from automotive store.

You have given only formula.

Surely you did enough simple arithmetic at junior school to know that if there are three things in a formula, and you have any two of them, it's 5 seconds work to rearrange the formula to find the other one?

12volt 12 watt halogen bulb is all you need. Ensure bulb does not touch any combustible surface as it gets quite hot.

Be aware that a 7.5AH battery will be rated for a c/20 amp discharge, 7.5/20 ie 375mA

So if you are discharging at 1 amp which is c/7.5 you will probably get no more than 3AH out before it is completely discharged.

SLA batteries do not appreciate discharging more than 50% (some will say less) otherwise their performance deteriorates further and they must be recharged immediately after discharge, to prevent permanent damage.

If the battery voltage drops below about 10.5V, you absolutely must immediately recharge it to prevent
a large loss in capacity and performance. Lead-acid batteries are very easily ruined by over-discharge, and
should always be stored fully charged and topped up regularly in storage (every month at least).

I'd recommend never discharging below 11V at at all possible.